What is WOW Endgame & WHY is it so special?

So I only started last year, so I do not.
People convinced me, that for most, it’s about the destination and not the journey when you’ve been a long-time player.
I just never imagined people would still want to play a game once they tired of the journey.
I thought people who were tired of leveling – just left.
I wanted to know what was at this destination that made it so appealing. Usually when my power is maxed, a game is no longer fun to me.

I do understand that a geared 120 is WAY more powerful than an un-geared 120 who just took whatever soulbound items they got from questing.

The question in my head is – why do I want to bother amassing all this extra power?

I am gathering this is for group raiding and pvp.
I’ll never enjoy WOW PVP, so I guess it would be raiding for me.