I could support that, if it would be bare subsistence, no recreation or books, no bodybuilding, no computers, no videogames and no TV.
And no discretion for any court at any level to claim jurisdiction over the administration of any state prisons.
Congress has the power to limit even the jurisdiction of the Supreme court, in matters not clearly Constitutional.
Congress hasn’t done that, and it would be politically unpopular to create a special situation where grievances would have less avenue to be addressed than others. It would be seen as rolling out the red carpet for abuses.