> If you (plural) can't write a one line answer to a bug report or click a reject PR button, then why should I put any effort?

You wrote a PR because you benefited from source code that somebody on the internet shared for free, and wanted to share that work for free as well. See the PR as just one way to open source your patch. You could put it on your blog, in an email list, or keep it in a fork.

By opening a PR, you make it visible to other people who also benefit from the project and who may be interested in using it.

> then why should I put any effort?

Something I really want to say about this: if you decided to open a PR to an open source project, it is very likely that you put less effort into your PR than the other put into the open source project. But they gave it for free without complaining. You don't have to do it, but you can. And you will still have put less effort into it than the author.