When you have a big system, the most consistent argument against working on one thing is that you should be working on something else, this is true for everything in the system, because everyone has a different opinion on what that thing is.

For example: why should you spend time working on the playlist playback when youtube could instead spend time working on automatic categorization, content creators have to manually create playlists, even if they sequentially number their videos. Youtube shouldn't waste their time on playlist editing when it could be doing the right thing automatically.