20 years? More like somewhere between 30 to 40 if we count early WWW and the Gopher+Usenet that came before it. The GPL isn't quite that old, but the spirit behind it sure is. If we count early home-computer clubs back in the 70's (like the one that birthed the original Apple) or the ham-radio crowd that came before it, we can push into 50+ year territory, easy.

I hadn't considered AI being a paywall around the whole WWW but now that you mention it, it kind of looks that way. I've opined elsewhere that social media companies (e.g. Facebook) are building walled-gardens to keep eyeballs and attention-spans locked on their brand of reality. This would just be another avenue of attack in that strategy.