I'm probably the only person who doesn't mind it. I got Jarate, but that's it so far
R.I.P. achievement servers, is basically what it comes down to
The random system is the only thing Valve could do that could not be gamed by players or server owners (and they mentioned that a few times in interviews as a concern). Everyone gets the stuff at the same rate, presumably, whether you try to cheat it or not.
Also, achievement servers invalidate achievements themselves, turning them into a chore instead of something interesting that happens during play, often performance based
Valve put the time into coding the achievements, they wanted them to be used for their original purpose
Last, I'm sure Valve has their reasons for releasing content gradually instead of all at once. Getting you to play more is probably a big part of it