i wrote a big comment about it some time ago but it got swallowed up by the fact that anything older than a month won't show up in your post history in order to not have the site crashing down, will reply later with an actual answer, i'm super tired rn, but to give you a short answer, colony-founding was a specific activity that was engaged in only by the largely disunited city-state societies that could only thrived interstitially in the areas of the world where the big empires didn't care enough to extend, it's why the Greeks, Phoenicians, and later the Carthaginians started colonies, but conversely the Persians, Egyptians, or Romans did not engage in colony-building. you could argue that none of them had naval capacity which is true: the Persians largely conquered the Phoenician city-states and used them as a client navy with them focusing on land forces, Egypt was largely Nile-oriented and didn't need to expand, really, Rome eventually built a navy but didn't use it for colony-building; you could argue they had soldier-colonies, but i digress

here's a novel way to look at colony-building in the classical antiquity mediteranean: land travel is limited to a radius of about 150km, if you have beasts of burden packed up with the maximum amount of fodder they are able to carry, they would eat that fodder in about 150km, and that's even before you actually carry anything of value, so resupplying posts need to be placed at 80km intervals, what's more you can't just resupply on fodder indefinitely, you're trying to turn a profit here; the army more or less doesn't care, even in ancient times, most settlements had some sort of commissary that made sure there were excess supplies for armies coming and going (the 150km rules applies to humans just as well as it does to ancient-breed oxen or donkeys)

so you need something more efficient, river transport is almost free, at least the one way the river flows, but the rivers are not open for navigation all year round, during heavy rainfall they flood and become unnavigable, they might freeze in winter and so on

ultimately, sea transport was that era's rail tracks, and building ports was akin to building more train stations, sure, you need to stock up on food and water for the crew in excess of your cargo, but you benefit from economies of scale: a ship then times larger does not need ten times as much crew, generally with bigger ships you can get away with less crew relative to the amount of goods you're carrying

we even have some kind of written record of this, from Diocletian's Maximum Prices Edict set the relative cost for transport we can deduce that if sea transport costs you 1 unit (the base ratio) then the cost of river transport is 5 times more, and the cost of wagon transport by land is 28 / 56 times more (there's 2 numbers here because of the posibility of translating this bit in two different ways, but don't worry, they're both huge numbers so it doesn't matter) all, in all while not absolute ratios, they can be seen as orders of magnitude, exact costs depend on distance, terrain, conditions of rivers and seas, weight of goods, precise animals used, and technology

of course a lot of this trade already happened in the levant between egypt, mesopotamians, hitties, minoan greeks, so on, so you should ask yourself, why would they ever want to trade with largely nomadic european dirt farmers? well, the short answer is, the proliferation of iron tools after the bronze age collapse made the rain-watered fields and hills of europe much more productive agriculturally speaking, meaning the european continent, which as far as ancient history is concerned is completely irrelevant, now has a healthy surplus to start trading for other goods

FINALLY, a short aside / rant on agriculture: it's not like in civ where people just "discover" agriculture, like yeah, you put the seed in the ground and it makes food, genious, the big problem is soil eventually depletes, and it does so very very quickly, in fact, especially if you have no conception of fertiliser, no way to dig up soil (with a plow) so that it can replace the now depleted top soil (or even conception that that would help), no consistent way to get water on your crops, and so on, on most european soil that means you get one decent harvest (if at all), and the next one on the same plot is basically dogshit

we're pretty sure most gatherer-hunters were aware of rainwater agriculture, they just didn't think it was worth it

the first literate agriculturalist communities formed around river valleys where 2 of those problems, water and fertilisation (the silt of the river replenishes your fields through the flood season via the irrigation you built), but honestly, there are not many places where this happens, except for the nile, mesopotamia, the indus valley and the yellow river

with bronze tools, european nomads could now cut down / debark trees, slash bushes and other smaller plants, let them dry for a couple months and then set fire to the now dried cutland fertilising the soil and meaning they could get reliable harvests for about 5 years max out of that plot of land (this is a upper estimate and does suppose you use some kind of tool to plow the field (as much as you can, you don't have the tools to remove the tree stumps yet)

this 5 year upper bound means that yes, in 5 years the settlement would eventually be deserted, although realistically, your second harvest is smaller than your first so people would be enticed to leave for the next slash and burn plot of forest as subsequent harvests yielded less food

iron tools made it so tree stumps could be removed and plows could dig deeper into the soil, overturning deeper soiled that was not depleted meaning that rainwater agriculturalism (contrasting with alluvial agriculturalism) was actually viable and that people engaging in it could have a sedentary lifestyle and didn't have to be semi-nomadic

conveniently enough this is what the greeks and most of europe came out of the rainwater agricultural "revolution"

PS

most boat trade was tramp trade

it's not that iron tools were better than bronze tools, in a lot of respects bronze was quality-wise, better, it's just that bronze was made by smelting copper with tin, with tin being pretty rare and hard to come by, making bronze scarce, check out bronze age nomad axes used to cut down trees, their blades are like an inch wide, no way you're getting enough of that to make a plow; iron on the other hand is fucking everywhere and once you have the high-heat kilns required to smelt it, it is plentiful and cheap, meaning iron tools get to spread far and wide equally

anyway yeah, shit's complex, if i had more time i would have written a shorter, less rambly, more to the point reply

edit: oh yeah i forgot to actually link it to your OP, if someone says ancient era and modern age colonies are the same they have no idea what they're talking about and you should tell them they have a discoloured patch on their face that looks like the start of BOFA