OP i have news for you.
A lot of the time they do know the mechanics they just choose to ignore them.This is because of 2 things.
A lot of players have attitude of i will dps and the other dps will do the mechanics for me.What happens a lot of time is several people have same selfish ideals so nobody does the mechanics.
Due to there not being proper Ilvl restrictions on older content and because most people now clear older content through level unsync you have a large player base that is brought up on the ideal of if you dps hard enough you can skip mechanics and never bother doing or learning them.This had been going on since Heavensward.

The only way to fix these issues are for SE to remove unsynced runs from game completly and have harsher max ilvl restrictions.