Genuinely, why do people main creatures they don't own?

I see posts on here all the time about people complain slots they don't own died. And I can only imagine the shit ton of mush they put into having that creature as their main.

I imagine they would be a little closer to just owning the spec they want if they weren't putting thousands into reviving it over and over again or restarting the slot.

I feel like I'm missing something bc it Dosent really make since to me that anyone would play something they don't own. Even though this game involves lots of pvp and they know they're gonna have to pay for the trail (+ to keep their muts sometimes) over and over again.

Genuine answers to why you play a creature you don't own are appreciated.