I think other issues that are relevant are 1) the length of the session, and 2) the impact of actual play shows.
If you are playing 8-10 hour games, or longer, like we did when I was in high school, then a bunch of encounters make sense. But if your sessions are 2-4 hours, which I think is more typical, especially as we get older, then having a ton of encounters becomes impractical, and carrying the adventuring day on between sessions, while sometimes necessary, is not really optimal. So that puts a practical pressure on how many encounters happen during an adventuring day.
Then there is the impact of watching actual play shows, which I think are increasingly influential on how many think the game is optimally played. If you watch an episode of Critical Role, there is typically one combat encounter over a 3-4 hour session. Sometimes none. The emphasis is very much on story and character, and as all of these people are entertainers first and foremost, it makes sense that combat encounters are not a priority. So this normalizes a low encounter session.
And I stand by my assertion that D&D combat is kind of slow paced and often boring. Players often tune out when it isn't their turn, and a fairly straightforward combat can still take an hour to resolve, particularly with a large group.
When I incorporate a published adventure into my campaign, the first thing I do is eliminate at least half of the encounters. Most of them are a waste of time and don't advance the story in an appreciable way. But this then absolutely impacts the degree of challenge. Usually I compensate by making the meaningful encounters more dangerous, but this an art rather than a science.