And yet, the game system doesn't do a single thing to discourage or even imply, in any shape nor form that this isn't completely acceptable as a form of play.

In fact, given that the characters lack a house, lack any form of rental accommodation in 5E at least, they're hobo's by mechanical necessity at character generation. They have nothing to lose by just rolling onto the next town.

And then there is "murder as a solution". Which is actually the game recommended solution for almost every single other opponent. Given so many tools to kill and so few social tools, is it any surprise that some players take the system at face value? Is there a single bit of gear which provides a bonus to being social? Any feats that make you better at this?

They are so few and far between that the system may as well endorse "You're gonna fight things, might as well use it as a first resort."

Then DMs are encouraged to balance encounters so that PCs will find it fun, but not deadly. If you had no idea if you were going to live or die in a fight, you'd be less willing to randomly pick them. Having a dockworker who is a retired adventurer and 5-8 levels above the party can put a serious crimp on any random low level fight.

Dungeons and Dragons does nothing to suggest that straight up killing everyone is a bad thing, or something that's bad for your character.