I frequently perceive a sense of entitlement from drive by PR contributors, as if they are giving a gift to the maintainer, when in reality, it often takes more time for the maintainer to test, review, and give feedback on contributions than if they’d done it themselves.
I imagine the people spamming repositories for a T-shirt are the same people who will harass maintainers to “just merge it already.”
This means not all os projects are likely to yield you a t-shirt, but it does mean your contributions must be good and relevant to have a chance.
There is some technique to reviewing a project and knowing what is likely to be pulled based on its context.
That aught to cut down on it.
Fwiw, DO should be doing something for the projects that accept a PR from this “fest” either t-shirts or a donation to a foss advocacy org or similar.
However, I don't see how that works with a hackaton mindset.
If that's what you think then why accept pull requests at all on your project?
And on balance, I love open source!
It’s just one of those unfortunate things where it’s hard and slow to be considerate while being easy and cheap to be inconsiderate.
They probably should validate a somewhat matching commit with the same e-mail address ending up in a branch or something. Few if any projects modify those.
(I maintain a handful of small libraries that meet your description, and only recently "awakened from slumber" to release a new version of https://github.com/hunterloftis/throng after five years)