Why the PS5 should be backwards compatible with all Playstation consoles

[Pemalite]

WolfpackN64 said:

The only reason the PS4 might be an issue is that the PS5 will probably use a newer version of FreeBSD (and thus newer, incompatible software libraries). But there are multiple software container platforms that can package the older PS4 libraries for the games to interface with.

Why not just virtualize the Playstation 4's software environment and execute PS4 code natively?
You don't need to worry about compatibility in the Playstation 5's software environment then... It's what Microsoft did.