As someone who plays the following regularly, I can maybe give some reasons:
Mercy boxing:
in OCE, we’ve built up a strong community in Mercy Boxing - almost everyone knows each other, and we’re all good friends. It’s also super fun to fly around and punch eachother?
YMYD:
I’ve made EXTREMELY close friends in this mode, adn while people get extremely toxic, it’s still a pretty fun mode - and if you git gud at it, it’s super ez.
500 everything:
it’s chaotic and fun. that’s really it
chill/kill:
it’s nice to relax after stressful games and just throw a dance party, or try match sprays with other people! it’s a good way to unwind.
Custom games are severely lacking in the features department. There are so many ideas being thrown around to make custom games interesting, but we are limited to basic tools. Basic tools create basic modes. I dream of a day that we can get more freedom. More infinite ults, the ability to use older builds of heroes, the ability to customize different variations of the same hero on a team, a map editor, and so much more. Until then this is all we got.
I made a mode where I nerfed, buffed, or outright changed a characters role (Overwatch - Code: Destruction) but no one wanted to join because the other ones are so popular.
You make custom games that end up getting locked-out because of an on-going bug (almost one year with this). What’s the point of making detailed modes when you end up losing them the next month?