No idea, maybe... i started playing again in legion after taking a break from WotLK and I can't say I noticed it becoming harder when someone tagged a mob. I know rares get higher hp and stuff to allow for more time for others to join in, which again is more community friendly to me.
And I rarely see, can't recall an instance, where people tag a rare and then leaves... most people stay and fight because it's quicker due to it locking them into combat.
The main point is that I can't understand the logic in that locking mob tagging somehow was more friendly rather than shared tagging. Can you explain how it would be more friendly? Only argument I can see is that it promotes grouping up, but that's just sharing with extra steps. A lot of grouping up for rares and quest mobs were just a silent party invite, kill mob, then leave with few or no words. People who wanted to talk, talked, same as now, people who don't want to talk, won't...same as now.