Playing wow on a PvE server is basically the following:
1, 2, 1, 2, 3, wand/autoattack - mob dies
Repeat literally 10,000 times
Things change a bit when you raid or if you make some friends. Then the enjoyment comes from interactions with others - it is not the game that is actually fun though
On a PvP server its:
1, 2, 1, 2, 3… wait I’m being attacked, time to use all the other skills/abilities in my arsenal. It is a challenge because you a fighting another mind and not a scripted battle. There is the excitement because you didn’t choose where / when this happened.
It also opens up entirely new experiences - you’ll find yourself pausing a quest change to help some guy in chat get revenge on his gankers. This can snowball into the epic southshore battles of old. On a PvP server the leveling experience is a lot more fun than end game because of this - on PvE it is a rush to level 60 because that is when the game “starts”.