Some good answers in here already. It boils down to a couple points for me:
- Back when I started selfhosting, it was either nginx or apache, and I found nginx better and easier to set up
- All the nginx knowledge I learned years ago still works just the same as it did back then, so why potentially mess things up by switching if it all still works
- Basically every project has an example nginx config for reference, that can't be said about other proxies
- It is easier to find support online for edge cases that might pop up with nginx due to the ubiquity of its use and years of history