In the long distant past of 4-5 years ago, it simply wasn't a problem. Few projects were overwhelmed with PRs to begin with.

And for the major projects where there was a flood of PRs, it was fairly easy to identify if someone knew what they were talking about by looking at their language; Correct use of jargon, especially domain-specific jargon.

The broader reason why "unknown contributor" PRs were held in high regard is that, outside of some specific incidents (thank you, DigitalOcean and your stupid tshirts), the odds were pretty good of a drive by PR coming from someone who identified a problem in your software by using it. Those are incredibly valuable PRs, especially as the work of diagnosing the problem generally also identifies the solution.

It's very hard to design a UX that impedes clueless fools spamming PRs but not the occasional random person finding sincere issues and having the time to identify (and fix them) but not permanent project contribution.

> and the hard part isn't writing code anymore but generating the spec

My POV: This is a bunch of crap and always has been.

Any sufficiently detailed specification is code. And the cost of writing such a specification is the cost of writing code. Every time "low code" has been tried, it doesn't work for this very reason.

e.g. The work of a ticket "Create a product category for 'Lime'" consists not of adding a database entry and typing in the word 'Lime', it consists of the human work of calling your client and asking whether it should go under Fruit or Cement.

Because until now, unknown contributors either submitted obvious junk which could be closed by even an unskilled moderator (I've done triage work for OS projects before) or they submitted something that was workable and a good start.

The latter is where you get all known contributors from! So if you close off unknown contributors the project will eventually stagnate and die.