In large it comes down to game design. if something can be ignored then it gets ignored.

if during a boss fight you can ignore the adds and just punch through, smack the boss and win then people will do it.
if you can completely ignore mechanics because the healers can keep you up then people will.
if you can hit hard enough to completely skip "phases" then people do.
if you can ignore half your skills / buffs and still clear content then people do it.

On the one hand everyone wants everyone to play properly but at the same time they want to take as many short cuts as possible. often see people play "properly" and then get crap for it. ignore the mechanics just zerg the boss!!!!