A large majority of their player base never uses mods (roughly 92%). They need to serve a minimum viable product to people who don’t know about or care about that ecosystem. They tried to bridge that gap with paid mods, but, well, we know how that went.
Agreed. Bethesda games are great for mods that supplement and tweak the experience to your liking. As much as it’s cool to get a few mods that add quests and such, the quality of those vary drastically and, as much as it’s fun to punching bag Bethesda quests, they hit a minimum level of acceptable and enjoyable quality, and the coherence of the world wouldn’t work with amateur/nonexistent/variable quality (both acting and recording) of voice acting.
It just wouldn’t be at all the same thing and wouldn’t appeal to the same people.