I don't think these game modes should be removed either. There is always a possibility for them to become more popular in the future, or to gain updates in the future. Also players have different shifts. When bridges and uhc first came out, people were on them all the time, then it got quiet, but who knows the players could shift back again especially with an update. As for oitc, you don't need a lot of people for it to be fun, it can be fun to play with 3, or 4 of your friends every once in a while. As well as Mob arena, personally I like doing mob arena by myself, I find it relaxing, but also sometimes a challenge at the same time, I can usually get to a pretty high wave by myself. Some games need updates, but as for removals, I don't think so.