Which clients do this? I think it’s intended to help new users. We should have options to set default feed though.
Discussion
So far the only one I know of is oddbean.
that's probably because it's meant to imitate Hacker News, and hacker news sorts by popular posts with most points.
I don't see this as a problem. This client is specifically mimicking another and this is the intended way of using it.
Sorting by trending / popular is a good way to show something interesting to new users. Even existing users might like it. But, it shouldn't be the only way. Clients like Snort / Iris already let you customized your default feed view (others too probably, I haven't checked). I think this is a good balance - ability to set what you see first.