With respect, there is so much that is unrealistic about the fantasy genre that just invoking "realism" does not strike me as a coherent argument. This one item is picked out to stand alone among so much other realism that has been tossed aside, "realism" just doesn't communicate enough to edify others why death remains.
Especially when the game allows coming back from the dead, which is pretty arguably less realistic than having absurd luck to not die in the first place.
So, I'm going to push back on this. "Realism" is at best so oversimplified as to not communicate what is important about it.
You still seem to be treating realism as an all or nothing thing and it's a spectrum. Many spectrums, really. When we use the realism argument, we are not tossing aside any other realism and picking it to stand alone. This is just the topic now.
The game is full of realism. Swords are made of metal, have edges and do slashing damage. There are trees. Humans are shaped like humans and breathe air. Realism is everywhere and we all have levels of it that we prefer that vary depending on what aspect of the game we are looking at.
I will agree that it's hard to communicate what exactly realism means to us as individuals. There no concrete number that we can assign so that others can understand what we as individuals are comfortable with. All we can really say is that X thing in the game is not realistic enough, realistic enough, or too realistic for our tastes. The inability to communicate what realism means to us as, though, doesn't mean that it isn't the reason or the primary reason we have. It's a tough situation. It's the primary reason, but it doesn't communicate enough. I'm not sure what the solution is.
Now I'm going to push back a bit on coming back from the dead being less realistic than absurd luck. In a fantasy setting if something is called out as being an exception to our reality, it becomes a reality of that setting. A sort of fantasy realism if you will. Magic is the single largest example of that. A wizard casting fireball in D&D has fantasy realism, so it doesn't conflict with actual realism. We've accepted magic as "reality" for the sake of the game.
Coming back from the dead would be highly unrealistic if the dead just woke up 4 days later for no reason other than it's a rule. Casting Raise Dead, though, is perfectly realistic as part of the fantasy realism we accept for the game. It will be more "realistic" than a bunch of coincidences happening throughout the multiverse allowing you to send messages from other planes, worlds, isolated islands, etc.