How do you cope with coworkers who are okay with lousy code and don't want to make it better because "how does it matter"?

.

Your only option usually is a better environment. Start off by collaborating with people on OSS that actually care (they wouldn't do it as a hobby if they didn't care). Build up your resume while being persistent while working and standing by your ideals.

If nobody changes, try to implement systematic changes that encourage better code quality (this can be done simultaneously as the above). PRs, pair programming, daily standups, make the environment more welcoming and agile. Also encourage people to ask questions and that no question is truly stupid.

If people don't take (it happens), then you need to change jobs. Try using connections you built up in OSS communities, or use something like Upwork/Indeed (depending on whether or not you want to Freelance or be employed respectively, although I got long term work through Upwork).

And take risks, it's easy to stay in the same place when it's comfortable, but it's probably taking more of a toll on you than you think.

Force 'em to implement a bunch of bullshit feature into their bloody malformed code structures.
Maybe, after a while, they will try to improve it ^^

@TylerDDevRant don't know if this will work but sure sounds fun XD

Teaching.
Barring that: Murder.
Barring that: Remorseless ridicule.

If the above does not work: Quit.