I think the op question is phrased wrong. It's not about how often PCs SHOULD die. I think many of us GMs cheer on our party and don't want anyone to die.
It's more about the possibility that PCs COULD die. I've played a lot of Savage Worlds over the last years, and even if it's not a super deadly system with Bennies etc it's also a very swingy system where death actually can happen.
I agree that this is more about how often PCs could die but there are game systems that practically guarantee a very lethal game where you go through multiple characters as the norm.
But lately I've become more and more invested in DCC and OSR games. And a big part of that is that it's simply more fun and satisfying for me to GM games where PC death is a real risk and motivating force for players to be smart, tactical and not hobo rush every encounter, and instead seek smart ways to handle encounters.
With GM work and house ruling you can work real risk of death into any system, but it's not how for example raw 5e is constructed.
I disagree with this. Level of lethality in D&D games of all editions has largely depended on the DM and group and always have. Combats in my games vary significantly, sometimes it's rush into the burning building to save the day, other times one or more PCs will die if they don't take a careful approach. I will clearly broadcast if a super deadly combat is ahead or provide an escape route. My players know me well enough to believe me and plan accordingly.
