Since then there has sprung up a fetish for bureaucratic process, and tooling has arisen to foster that, such that the barrier to entry is significantly higher now than it was in the 90s. All you needed was a text editor and an email account. Now you need accounts on whatever code forge is involved, and you didn't write enough unit tests, and you failed to properly format your pull request, and what do you mean you're not an expert in whatever version control we've adopted? This pull request sat in an open state because you didn't tag it appropriately. The CI system was updated and your code wasn't covered in the automated integration test, please resubmit after making minor punctuation changes in a metadata file.
Over time, this stuff filters out contributors and leaves a core of people who are comfortable with the structure of the engineering process for that specific project. It's not a bad thing that engineering standards are higher, but it's no longer a world of people 'scratching an itch' -- there's yak shaving to be done, and the number of people willing to shave that yak has always been smaller than the number of people who are not.
I don't think the author is right about things having been harder in the old days led to a higher proportion of the internet being qualified to contribute. I think it's much harder now to patch software upstream than it ever has been.