Because the modes are casual, I should be able to have a bit of fun, some games will be easy, some games will be harder. I can experiment with different styles, loadouts whatever. SBMM in casual modes ruins this, because every game turns into a sweaty slog.

You also dont improve at games past a certain point by killing bots and players just as bad as yourself. I got better by playing against and with the better players, the lobbies were more diverse which was more fun and better for learning.