IMO, I think Automattic introduced Gutenberg way too soon to Core and introduced it as very half baked. Still to this day it's very half baked to an incredible degree, some pages will just break outright and resort to JSON errors, not to mention the built in blocks are awful and 3rd party blocks often break. That probably turned off a lot of people. It's still easier to just buy a theme that has a built in page builder and you'll get similar Lighthouse scores to Gutenburg (this being for average users, not custom themers, etc).