> It was always heavily moderated

No, it absolutely very much was not. Even granting that you mean actions of the community (what we call "curation") rather than the small and extremely strained moderation team, way too much stuff historically got through, while people yelled at the OP in the comments and argued over downvotes instead of taking the action that actually matters: voting or flagging to close the question. Worse, people would post answers that acknowledge the problem with the question and asking OP in the answer text to fix things.

I know because I was part of that mess back then, because I didn't know better. That, in turn, was mostly because the entire set of ground expectations was poorly communicated, and the community wasn't given the tools to improve that communication (e.g. couldn't edit the help pages, had their feedback about the discoverability of site documentation ignored, etc.). But it was also because Atwood and Spolsky hadn't refined their intuition about why beginners' bad questions are bad. (Hint: it is not because most of their problems are easy to solve, or "beneath" experts.)

> when following a StackOverflow link from Google

Google got worse at search over the years, so you ended up seeing low-quality versions of the question more often. And the site got way too big (there is no reason why there should be more than three times as many publicly visible questions on Stack Overflow, as publicly visible articles on Wikipedia), such that search results could get diluted with irrelevant low-quality questions that happened to have a lot of keyword overlap with what you wanted. And misleading questions didn't get cleaned up, so you would search for X and find a question where the OP hadn't tried to analyze the situation at all and ended up asking about X when the problem was actually Y, and got the question closed as a duplicate of the main Y "canonical". (I know because I used to lose considerable amounts of hair trying to find the X canonical that I knew was there but stubbornly refused to turn up in searches.)

If "moderation" had actually "always" been "heavy" then you wouldn't have had this problem because this stuff would have gotten hidden from public view, one way or another.

> a moderator shutting it down

Again, these actions are overwhelmingly not taken by moderators, and phrasing things this way reflects a refusal to interact with the community on its own terms and understand its policies. Those who hold an outsider mindset are bound to end up feeling like outsiders.