One situation where I've done this or seen it done is where the early game (for a character) is meant to be high-risk but low-investment. In a game where there's PC death and you restart from scratch (for video games this might be like a roguelike), this gives you the feeling that life is genuinely dangerous for newbies and that the characters who survive have risen above a crowd of average characters; for games where permadeath isn't an issue, this can give you some nailbiter experiences early on. In either case, these are experiences that quickly overstay their welcome, so the game wants to bootstrap you out of that stage pretty quickly.

Lategame levelling can't rely as much on significant growth and radical changes to your quality of life, because no game can really offer enough breadth to give that experience constantly. Games that try tend to be treadmill experiences, and these can be unsatisfying to players. Thus, lategame levelling tends to be more sedate, and spacing it out farther can be a way to ensure that when you do level, it still feels like a meaningful advancement.