There is a difference between "not seeing the problem" and "asking yourself what are the implications of it". I'm running 15+ instances and I'm running a website that is devoted to help people find the "canonical" community in the fediverse. I can point to dozens of other issues that are a lot more "painful" to me as an user and an instance admin, none of them are related with the "pain of having to choose which community to join or focus".
I'm again going to ask: is there any actual, practical example of this being such a "huge issue"?