Because a lot of this stuff is a social signifier more than a bonus. Aka, if you are in a raiding group and only 5 of the team has grinded out sockets, it's a signifier to everyone that they are the ones willing to put in the time to give the group an advantage, however small, and everyone else is not.
there is a social component to all of this stuff beyond just numbers.
(though that said, this entire game is about adding on many small bonuses; skipping out on a few doesn't really matter, but it adds up, especially if you want to parse well)