You missed the second part of that clause, which is pretty critical context.
> So unless you're really into just having fun - which the game mostly does not encourage in lieu of running dungeons and getting gear and etc
PvP most certainly falls under that umbrella in italics. Getting to grand marshal back in the day involved sinking copious amounts of time into battlegrounds in order to get a special title and some special gear. There was/is most definitely a carrot on a stick for PvP as well.
In contrast, players have never been incentivized to explore much. Maybe you get a title nowadays, but it's not going to be anything cool like 'Dreadful Gladiator'. There's no special sword for exploring every sector of Azeroth.
EDIT: Further thoughts
> if they don't explicitly give you a token for having fun with your friends, saying that they "don't encourage fun" is pretty false.
Why do you think it's false? It's implicit discouragement. In the thinly-veiled skinner box that is WoW, gear and tokens and titles are positive reinforcement.
It's not a huge leap of logic to say that positive reinforcement tends to discourage behavior that doesn't lead to the reward.