ROMs actually do exist for those consoles, just not here or in a big amount. I assume PS3 and Wii U archiving might start sometime in the near future since they're becoming obsolete, but I don't think we'll see a full archive for a few more years.
"NintenDON'T sue me please haha"
ROMS don't exist for these consoles because the services and games are still being actively sold by the respective company. The point of a ROM is game preservation and archiving, which isn't really needed for the newer consoles yet. That goes hand in hand with the legal gray area of providing copies of games that are still being sold.
So... maybe in 20 years there will be a PS3 ROM archive. Until the PS3 digital store is shut down and those games aren't available anymore, you won't see them here.