There are three possibilities as I see it:
1. Hubert is a bad coach and he rubs too many players the wrong way.
2. The roster construction has been poor, which may or may not be cured with an improved player personnel department.
3. The attrition is the result of changes in the CBB landscape and are not different in scope or kind than other major programs.
I think you believe the answer is just one of the three, as you write "there is something greater going on" as opposed to "there are several things going on." I think it is likely a combination of all three factors.
I think that there are several things going on that lead us to our current situation, including the 3 things you mention. My takes on them:
1. I don't think HD is a "bad coach" nor do I think he "rubs players the wrong way". I think he is a decent (namely inexperienced) coach at a program where expectations don't really allow for the failures and growing pains associated with decent/inexperienced coaching.
2. The roster construction has been less-than-optimal. Roster construction is ultimately a head coach responsibility and has been used as an excuse to cover for other, more significant, coaching issues.
3. The landscape of CBB has certainly changed over the last few years. An acceptable head coach for Carolina Basketball will be able to create and carry out a plan for success that takes into account those changes as those changes are largely permanent.
I'll be clear...HD as our head coach (due to lack of experience and, possibly, his ceiling as a coach) is the main issue with Carolina Basketball in April 2025. We can try to improve a number of other things - support staff, player development programs, NIL, HS & transfer scouting, etc - but (in the near term) as long as HD is the coach, Carolina Basketball is not putting itself in the best position to succeed because it is settling for a significant deficit at the head coach position over what the program could almost certainly obtain should it seek a new head coach.
When we try to isolate the symptoms - "problem" players, roster construction, changing landscape of CBB, lack of player development, slow starts, whatever - we can easily lose sight of one central truth...the head coach is the primary person responsible for addressing all of those things. And, while I am not saying you are necessarily doing this, there are certainly HD supporters who are intentionally focusing on the symptoms to avoid having to address the main issue: HD is significantly underperforming for the position he holds and the main way to address that concern is to obtain a new head coach. Because even if we address all of the symptoms noted above, we still are settling for a significant deficit in the head coaching position over other available options.