They really weren't though. Look at the core, fundamentals of each game. Ignore the second-hand motivations of Zero/background characters.
The doors were all measured so everyone could pass through every door. No one would be left behind, no kills required. Even the final door operated on this principle. Literally zero deaths were required for anyone put into this game to reach the end.
The only reason deaths happen in the main routes, as per Zero's plans.
Is because Ace is a scumbag; not because the Coded Door game required death to proceed. Even the time loop itself wasn't
requiring any deaths. All that needed to happen was for Jumpei to go left instead of right to get the code for the coffin to
free Snake, who was put there to AVOID him dying and thus opening door 9. Ace's murder spree in the left-door timeline
is due to his own wants, not because the game required him to in order to pass through door 9.
Again, stated outright at the beginning of the game. All everyone has to do to go free is press Ally each and every single time. Zero deaths required and they can escape the game.
Not that they can go anywhere AFTER the game.
Only reason deaths happen are, as per Zero's plans.
-Radical 6, which is an outside influence and has nothing to do with the mechanics of the Prisoner Dilemma game itself. It exists purely
as a 'cheat' to making unrequited killing far more likely and because it enables more advanced time-leaping.
-Dio is a dick.
Now...let's compare this to...
Game is you kill people to get passwords to escape.
See the dissonance now?
Since people like to reference the 999/VLR series as "X + Y + Saw"; lemme make another comparison.
999/VLR feel like John-Jigsaw traps. You're gonna go through hell, but they're DESIGNED to let you escape alive if you really want to.
ZTD feels like Amanda/Hoffman-Jigsaw traps. They're rigged to kill you, no matter what.
Makes ZTD feel like the mastermind might possibly have nothing to do with the prior Zeros because of that difference. A faux-Zero game.