Someone correct me if I'm wrong but I believe YouTube's new strategy requires frequent filter list updates but with MV3 the filter list is embedded in the extension so the extension itself would need to be updated (and Google controls the speed at which extensions can be updated).

For a long time I assumed Google's approach to hampering AdBlockers with MV3 was going to be the rule count limits imposed by MV3 but I think now it's more about controlling the speed that filter lists can be updated.