For me it's primarily to get away from Reddit's need to throw politics and social issues into every damn sub no matter if it fits on the sub or not. There is a time and place for everything.

For instance, if I go to a sub about games I want to talk about games and game related things. Nothing more. Now today /r/games shut down their sub for the day and put up some lecturing post about racism, sexism, and whatnot. Yes these are important issues, but not in a damn sub about gaming. All I did was roll my eyes and unsub. If I wanted to discuss those things I'd go to a relevant sub.

Another sub, I think it was /r/unexpected, did a similar thing except they dedicated the day to posting memorials to Holocaust victims. Remembering the Holocaust and those who went through it is very important. Not on a comedic sub.