No system is
actually flawless. That's pretty much impossible. It's far more likely the latter.
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.