Butter is NOT favored because most people had it in their youth, but because of its extremely distinct flavour.

"Unctuous" is certainly not specific enough, the reason butter (and ghee) is so delicious is its butteriness, i.e. it has a highly distinct taste. All properly rendered animal fats have highly distinct tastes and serve different purposes. Schmaltz tastes slightly of chicken, duck fat of duck, lard of pork, and tallow of beef.

But butter does NOT distinctly taste of beef, rather, it is reminiscent of slightly-aged milk (or, in the case of ghee, it may even strongly smell like certain kinds of aged cheese). There is, also, in butter, significant absorbed water content, and, to my palate, even a very subtle acidity that is not quite present in other rendered animal fats that give it a sort of brightness that make it work in things like butter-creams and other delicate or mild flavours (e.g. popcorn).

It is IMO this specifically "non-meaty" unctuousness that is the real draw of butter. Not some childhood nostalgia.

Wouldn't the preferred fat of a culture be spread between countries as they interacted then? Instead it has been fairly one directional with butter being adopted globally but other fats remaining niche (except Olive oil). Is that because of imperialism or is it because it is the best tasting one?

Today, I am one of the Ten Thousand [1] that learned you can make croissants with olive oil. Thank you for that! I've always assumed the laminated dough required solid fats, but apparently any layering of fat and flour can make flaky goodness. I am guessing that liquid fats are probably harder to work with, and croissants are already tricky enough to get right: but I must try.

[1]: https://xkcd.com/1053/

As a kid I had both lard and butter on bread. Bras with lard and onions is amazing. But also that’s roughly the only combination of that works. Butter is way more versatile.