Difference: companies are not pushing their employees to use stack overflow. Stack overflow doesn't waste massive amounts of water and energy. Stack overflow does not easily abuse millions of copyrights in a second by scraping without permission.

There have been lots of tools and resources that have promised (and delivered!) increased programming productivity.

Individual results may vary, but it seems credible that thoroughly learning and using an editor like Vim or Emacs could yield a 2x productivity boost. For the most part, this has never really been pushed. If a programmer wanted to use Nano (or Notepad!), some may have found that odd, but nobody really cared. Use whatever editor you like. Even if it means leaving a 2x productivity boost on the table!

Why is it being pushed so hard that AI coding tools in particular must be used?

Another difference: stack overflow tells you you are wrong or tells you and do your own research or to read the manual (which in a high percentage of cases is the right answer). It doesn't tell you that you are right and proceeds to hallucinate some non-existent flags for some command invocation.