Personally I don't think Twitter cares much about the quality of users' timeline.

Twitter doesn't provide any easy way to manage followings while keep suggesting people to follow, because promoted accounts will be unfollowed easily.

I am one of the user in the official popular users list in China region, but most of my tweets are Japanese. This kind of careless mistake should not happen if they had do a simple review before selecting me. I've ask them to remove me from the list, but they never reply.

They seems to encourage users to keep following, increase the quantity not quality.