In reply to Amor.

Exactly this.

WordPress used to be the CMS with which we developers were able to pretty easily create websites for clients. Clients who themselves shouldn’t have technical knowledge and still able to manage the content well (custom post types, custom fields, etc). And not mess up the layout/design! Even with some basic PHP knowledge you’re able to create the most diverse themes with any functionality. Using existing plugins, building your own or coding some templates. That made it so popular with developers. Developers made WordPress big.

With Gutenberg and FSE the direction is completely different: “let’s make a self-hosted Squarespace/Wix”.
One problem is that it’s much more difficult to create more complex templates/pages. The easy things (text next to an image) are easier, but the more complex things are much more difficult or impossible.
Another problem is that in my opinion Gutenberg and certainly FSE gives clients too much power to mess up the website.
And there is of course the transition problems.