I half agree with you. The problem with Psionics is that it's had multiple strong identities, and the fanbase can't agree on which one should have primacy. Dark Sun though... I never actually played a campaign in it, but I had one of the novels and both of the CRPGs. So those are what shape my mental image of it, particularly the latter. And I really don't know how they'd update it for today.
Maybe they could do it. Mad Max pulled off a good new movie in the "wasteland apocalypse" genre. But that's a rarity, and the genres that Dark Sun was building on are even more out of fashion than they were 30 years ago. Not to mention the many, many problematic elements that would either need to be removed or treated with very precise care.
Also it's not just the setting. Is Dark Sun really Dark Sun if you don't have scarcity of metal and elemental Clerics and Preserving/Defiling magic? But all of those would need in depth mechanical support for transitioning into a 5e framework. How do you even do Preserving and Defiling with the proliferation of arcane casters? To say nothing of the "everyone has a Psionic Wild Talent" bit.
I dunno. I have some fond memories of Dark Sun, but boy would it be a heavy lift to update it. Maybe some things just aren't feasible.