Why are developers not thrilled about making games for the PS5 Pro?

Has multiple reasons.
1. Graphics cards are not as strong as you think they are, the big next gen gpus are too big to fit in consoles and require way too much electricity to run.
2. Price has to be below 1000 $ or the console won't sell
3. Developers became lazy because everyone uses Unreal Engine and they don't have to learn optimization, or even making their own engines. Developers are simply less and less qualified because their game design schools teach them useless wrong bullshit.
4. The great processing power required to achieve this high of graphics require extreme high amount of cooling, which homeconsoles aren't meant to do. Ideally homeconsoles need watercooling but consoles need to be somewhat robust because it's still a toy in a sense. Unlike a pc.
The closest we came to next gen graphics was Red Dead Redemtion 2 with dynamic clothing meshes, dynamic weather transformation, etc.
The change that PSpro will change anything is low, at best it will increase the framerate slightly.
The chance that PS6 will change something is also low, because consoles are always at least 1 GPU generation behind on release to justify the building price. Based on what NVIDIA plans for upcomming gpus it does not seem like they care much about small size, compact designs or less power requirements, but instead go for even bigger power drains and chipboards.
Furthermore the chance that a next Xbox or PS6 will ever exist is low because the companies are out of touch with the industry and lose millions on profit every year. The only way they can come back in graphical power is if the chip industry has a design massive size-efficienzy revolution which is unlikely because the only revolutions happening in the last 10 years are in storage, not in processing power.