The way we all measure enjoyment in pve is based on loot drops. Which are random, redundant, and seldom guaranteed. Pve also locks players into certain classes and play styles. Defender, res lock, bow hunter for example. I can enjoy my self in pvp losing, getting no loot drops, and solo just by getting that one satisfying kill. Pvp allows for multiple classes, gear load outs, and play styles. In pvp your results are based on your actions. Maybe not winning but life and death is not dependent on others knowing mechanics.