Because I remember reading articles with rumors that Sony's upcoming PS5 will have backwards compatibility with not only PS4 discs, but ALL Playstation consoles ever.
So dust out your old PS1 and PS2 games because they are now usable in modern hardware.
But again these are only rumors and Sony has yet shed a light on PS5 news or anything.
In the end this is the reason I am holding out on buying my own PS4, in the hope that a PS5 would AT LEAST have compatibility with PS4 game discs.
PS4 backwards compatibility was mentioned in passing by Mark Cerny in an interview, so we expect the PS5 to be at least backwards compatible with the PS4.
Anything beyond that is pure rumor and is best to be ignored.
You'll just have to wait until they unveil the PS5 sometime next year to know for sure.
The solid state drive and backwards compatibility (at least with PS4 software) have been the two main talking points of the PS5 so far. That's sounds cool, but I'd also love to have a better controller with more usages involving pressure sensitive button commands and, assuming it'll have stick buttons, that they'll be more durable.