Apart from what acomjean mentioned already (which is definitely an influence), the ROI on such a hack is pretty low. The PS4 was released 3-4 years ago and the PS3 was discontinued anywhere from 1-3 years ago, both depending on your region. In any case, it's an old system and people have moved on to newer and shinier consoles.
The PS3 has also had hardware-less exploits in the past, CFWs were all the rage. It's not like it's never been exploited or anything. The ECDSA private key used for signing software was released, even.
Would be super cool to see this blossom, but I'm guessing most if not all exploits nowadays will be kept hidden.
 #henkaku @ irc.freenode.net
Ironically, I played more classic (SNES/PS1) and homebrew games than actual PSP games on my device. Nevertheless PSP "hacks" are what got me into exploring other types of hardware, and eventually jailbreaking iPhones when they were first released. I used to participate on an IRC channel frequented by George Hotz (geohot) and was present when the iPhone was finally jailbroken. For a device that had no app store or games at the time, this was a huge deal - and the homebrew scene quickly flourished.
I still get nostalgic thinking about how I'd spend my lunchtime in high school playing Tap Tap Revolution or SNES emulators on my iPhone...