Edit: Here a link to askhistorians which supports my post

The fun thing is that it is assumed the UK got one body and that all acts are in accordance with rationality of that body. You know, instead of viewing it through a material lens of class struggle and contradictions within a class.

Even if (for the state or in sum of pounds and all that) it was a net loss, then there are exactly those farms you mention, the subjugation of people for economic gain, the manufacturing of textiles from the produce of those farms within the core of the empire, benefiting the owners of those factories, benefiting the liberal factions associated with that, benefiting indirectly the citizens of the core and also giving the workers at the factories income that could be slightly above the income without empire bonus (which, spoiler alert, was mostly not given to the workers, but kept in the hand of the capitalists and associated groups).

Or to put it another way: Lignite (brown coal) is produced, even though it got a huge ecological and health cost, as well as many death in producing it - still it is produce for capitalist reasons and to secure "energy security" in the battle of major powers.

That said, the new markets the colonies delivered, the comparative advantage due to the stream of goods against the continental powers and all such are major reasons to keep up empire. Furthermore the cost of imperialism were a reason the East India Tea company (basically a libertarians wet dream) was founded and they curiously managed to turn a profit from imperialism.

While it is true that for some cases in the beginning colonialism can be a net cost for the state in terms of money, the full picture can only be seen from the material analysis of the actors involved, the people at the place and as always the material and social conditions.