I'm guessing just a shift in priorities. People felt panicked when COVID hit, and I imagine for most of them, learning about a new diet wasn't the most important thing.

Also, in some places, there were food panics, so people might have been less interested in buying keto groceries, as keto's heavy on meats, cheeses, and other things that spoil quickly.

Stress eating? I bet fewer people are dieting right now than last year.