Of course interesting things happen outside of mainstream deep learning. The problem is that sorting by citation count is a terrible way to look broadly at research, because mainstream deep learning is so hyped up that there are just way more people working in that area than in other areas, and with more people come more citations.

It's a shame because I think that other areas offer much more interesting and technical questions, but many new researchers are only exposed to mainstream deep learning because the enormous hype drowns out everything else.