I can't find older posts (I bad at tags!) where I've noted the lack of D&D having any lose condition except for character death or total party kill.

So I'm surprised today to find a couple of people pointing it out on the wizards 5E playtest forum! Okay, massive post, but I'll quote the relavant bit.

Now he also have another point, that without some things a TPK is the only way to lose in recent editions.

 Exactly - the person refered to wants characters who go neg HP to stay down instead of popping back up from heals. Thus its a kind of 'losing' that doesn't involve the character actually dying.

It's one method of trying to put in losing without PC death - not the only method. It's interesting to see the 'you can't lose without a TPK/PC death' being stated by others as well.