They could have a convenient command line submission process for new versions without requiring every such change to be an actual PR. A simple web server that takes a POST request and converts it into a PR behind the scenes would be simpler for users as well, as there's no need then to clutter up your own github account with forks of their repo (or even to have a GH account in the first place).

I imagine that having an additional server for a (somewhat understaffed) project run by volunteers introduces additional costs and additional maintenance burden.

The current process is already convenient and all you need is a GitHub account. Having the account adds some identity or semblance of it at the very least. Without that? And with an additional server? Seems like a much wider attack surface compared to what's there now.

Thats what their GH action effectively _is_. They just used a poor choice of tool. They could write a program and host it on a web server and it still might screw up.