Going to take a guess here....I'm not saying that 5E combat is toothless and rigged so that death is unlikely (if not impossible), but that certainly seems to be the assumption at my table.
The party was fighting a gang of harpies in the last gaming session. As the monsters were approaching, right before rolling initiative, I asked someone for a History check. I ignored the result and informed them: "You've heard stories of these creatures, and how they delight in pain and suffering. They've been known to 'sing along' to the screams of their victims as if it were music." I paused for effect, then broke the fourth wall: "They are the sort of monster that will keep attacking you even after you drop to zero hit points, so be careful."
Everyone immediately put their phones down and sat up in their chairs. The assumption, up until that point anyway, was that combat wasn't anything to worry about. But now, things just got real...and it was just a random encounter.
In previous editions of the game, especially the Expert Rules of the 1980s, characters actively avoided combat. It was a last resort, something that happened after stealth and negotiation failed. It was far more risky, and resources were far more limited, compared to any other edition of the game that I've played.
And then they proceeded to nova their way through it if there was ever any risk or if they expected to be fighting harpies over & over again they treated the rest of the session like they were running through tomb of horrors.