So, on most systems nowadays, retail software is encrypted and signed with entirely different PKI from developer applications. You would have to obtain cracked retail software first, then resign it with your own keys. This is how you run pirated iOS apps now, which is only possible because Apple hands out developer keys like candy. It'd at least be theoretically possible to do the same thing with a console devkit and decrypted games.

This is also narrowly considering only the example of someone trying to pirate new releases for that given system. More broadly, the console manufacturers have class solidarity[0], and don't want you doing anything that might be a copyright violation - even if you aren't hurting them or their developers specifically. You could port over an emulator and steal older games, you could modify new games (even ones you own), or you could make fan games. They want absolutely none of that on their hardware, and the only way to guarantee that is to make sure everyone who touches a devkit is wearing contractual handcuffs.

[0] Vaguely Marxist term for "these people are in the same social situation, therefore their interests are aligned"