I assume those ideas were formulated around 2000ish, when humanity's smartest computers were at best as smart as nematodes and incapable of using language convincingly. Now that humanity's smartest computers are as smart as an ant colony, it turns out that with enough data they can use human language convincingly, which is very interesting but nevertheless a serious challenge to existing ideas around copyright. It's not enough to completely pull up the drawbridge so that humans can't freely access the data. But it's reasonable for a community-driven org like SO to be concerned about fundamentally dumb robots like GPT-4 threatening their survival and their mission.
Let me add that Google and OpenAI are fully aware that their tech is useless in the medium-term without technically-skilled humans contributing actual human thoughts to places like Stack Overflow.
Let me add that Google and OpenAI are fully aware that their tech is useless in the medium-term without technically-skilled humans contributing actual human thoughts to places like Stack Overflow.