The dose makes the poison. Do you remember when digital ocean (or someone similar) did that promotion thing for opening PRs/contributing to open source projects? It was a nightmare for maintainers because they were inundated with outright spam and also well-intentioned but poorly executed PR attempts by hapless newbies.
I think one reason that open source even kind of works is because "people contributing to open source" has a shit-ton of positive selection bias "baked in". The type of person liable to open a PR to an open source project is probably several standard deviations (or, at least one, right?) above the average developer. So that probably has the general effect of making reviewing a random cold-open PR less onerous of a task.
But if we cross into a world where the average value of a PR opened with a project drops substantially - either due to AI or due to a permanent advertising campaign from some company rewarding badges for opening open-source PRs - I wouldn't be surprised to see lots of open projects close/ignore github PRs and start doing something that looks more like how Linux handles it, where it's a lot more social-based and puts some of that positive-selection-bias filter back in place.