Why keep DF off of new content?

[Felis]

And when the heck did it everyone that uses DF become "the worst players in the game"

It is not really about worst players, but PF is the better way to learn and train new hard content.

static = players you play with regularly and learn to coordinate the playstyle together
PF = more or less random players, which you might play in future together again, can add them to friendlists or linkshell for other contents if you like how they play
DF= random players from other servers you pretty might not play together again after that content ended.