I think it's mostly a hold over. I suppose you could argue uniformity, though that's really just among combat classes. Crafters and gatherers get CP and GP instead of MP, while everyone has TP since everyone can at least sprint.

With the class system everyone can use mp (as any combat class -- not job), and yeah 1.0 made use of mp in many more ways than 2.0+. It's funny, one of the first classes I leveled (a bit) was CNJ so that I could have cure, protect, and raise on all future classes while leveling. I thought that would be useful (turns out DPS don't even have enough mp to cast raise unless you meld piety somewhere).