Well let's not forget that WotC wanted to make a ton of money on bringing in people new to the game. And the best way to do that is to not make it overly punishing, to drive away people who rage quit due to dying a lot in the early levels.
No longer is this a game where you are expected to bring a stack of character sheets with you, and that's the way WotC wants it.
That the system's death and healing rules reinforce this at a basic level will eventually drive some people away from it, towards games that are more lethal and risky than 5e, and unless there's a big push from 5e players for that kind of game, the "big fun" edition of D&D is here to stay.
Or, if you're a budding amateur game designer, I guess you could massively hack the game, but I doubt a couple of simple houserules would be enough.
The way I see it, 5e is a game that expects everyone to reach high levels and "win". So there isn't really a difficulty curve that separates the casuals from the hardcore players. You play long enough, you're probably going to hit level 20, have some big endgame adventure, then go back and do it all over again.
Well, except for saving throws. That's a "fun" thing to see, when someone realizes to their horror that they are designed to have three-four bad saving throws, and they're asked to make a DC 19-21 Charisma save or something. But I don't see that as a difficulty curve; it sort of sneaks up on you. You're doing fine, rarely having to make many saves, and then one day you run into a powerful enemy and you get mind controlled, banished from this plane of existence, or foiled by a high-level illusion and then realize there's not much you can do about it (except pray you survive til your next ASI and take Resilient, unless you can't...).