I think it's down to bone idle laziness for the most part.
If people really want to do it then for the most part they'll just do it. Those that don't make excuses.
I think you've just described my 2024. Must get back into the habit, and the saddle, in 2025.
Incidentally, I haven't really noticed any change in the number of commuters round here. Perhaps see two or three bikes each morning and the same in the evening and that hasn't changed much. It isn't really commuting territory.