Considering how the modding community made Skyrim a long-term success, this would be a very foolish decision.
You say that as if it removes the possibility but I don’t think I need to provide specific examples of obviously foolish decisions ruining modern games. There are plenty to choose from.
Oh absolutely, and Bethesda is absolutely capable of that. It would be very myopic for them though. They can’t possibly be ignorant of the fact that modding is what kept Skyrim selling for a decade.
Preventing modding would be a substantial exercise in hubris (“we don’t need them”), or one of those intentional failure/tax writeoff things.