Most of the time it's just sloppy. It's techno babble, but fantasy. Instead of "Reverse the polarity so we can hyperjump our warp drive back online!" it's "Reverse your mana flow so you can teleport through the aether!"

A lot of fantasy creators don't think their ideas all the way through. Like if you can make infinite fire using magic, you have an infinite energy source. If you have an infinite energy source, you have an infinite number of lanterns, transport systems, and so on. This also means there's not going to be conflicts over energy. Instead, we get people throwing fireballs at one another with some other techno babble reason for why there aren't free electric carriages.

If magic is unknowable and dangerous, then it makes sense why there isn't free drinking water everywhere from infinite ice/water mages.