Item Level too high

[Bixby]

Perhaps it is to facilitate the implementation of iLvl checks.

If iLvls are of small increments (e.g 50 for AF 51 for AK 52 for DL) it will be hard to accurately set iLvl restriction for dungeon content as it does not take decimal into account

There's this. Larger iLvl increments mean content with iLvl requirements allow a broader range of gear that can be mixed together.

It's also to encourage people to actually upgrade. If the ugly hat were only +1, more people would choose to be pretty than when the ugly hat is +10. (Oh sure, you're super-smart and look at every stat and do all the math, but remember, you're reading a forum dedicated to the game, let alone posting in one, which means you're putting much more energy into this than the average player.)