Because people are just playing the game and part of playing the game is actually using your abilities.
And the fact that these mobs are named or elite in some way is even more reason to actually pop stuff and kill it before it can potentially start hurting you.
Now, I get that world stuff is trivial in general and no you don’t really need to do this, but come on, let people use their buttons. If there’s an annoyance with respawn times for others to get the tag, that’s a Blizzard problem they should resolve, not a player problem.
Not saying it wouldn’t be nice if people waited if they saw people nearby that might need it. But expecting that to be the case when they’re also just playing the game is silly. They’re not grouped. They don’t know what the other people in the zone are doing or what they need in that moment.