I believe a lot of it, especially new bike owners, want the peace of mind of less mechanical hassle. Besides rear derailleur hangers breaking, front derailleurs as a whole tend to be fussy.

Now I’m not saying 12 speed is greatly better because one barrel adjustment off on a 12 speed and you ruin it but if it means you have one less component to worry about and a more “spacious” cockpit without the shifter, a lot of people are going to like that.