In 2016 SSDs weren't extremely common (or cheap) yet, and on top of that CPU speeds were irrelevant to consumer demands. 4K was becoming in demand as well as PSVR was being developed, hence the Pro making sense to create.
It's very interesting reading these replies completely failing to understand marketing. 95% of consumers buying consoles do not care about "oh the CPU is so weak" or "oh it's using dynamic resolution" or "oh the Ray tracing support isn't good". People DID care that they just spent $1000-$2000 on their brand new 4K TV and the PS4 only outputs 1080p at best and "looks blurry". So it serves a purpose even to those not tech-savvy.
On top of that, saying the ray-tracing support on a PS5 Pro would be dramatically better is kidding themselves, RDNA3 cards still have pretty crap RT performance at the lower end of the card lineup (although a step up from RDNA2), it be a minor difference at best, especially considering this would be an APU focused on efficiency and not a dGPU.
You can cope all you want, PS5 Pro would be ultra-niche, which is why I still don't even believe this is a real product. Someone here assumed maybe 20% of PS5 owners owning one, and that's an incredibly generous number. I cannot imagine the general public giving a shit in the slightest about a PS5 Pro, especially considering a good chunk of PS4 owners probably just upgraded with Spider-Man 2.