I’m painfully aware.
A lot of ‘goofy, nerdy, tinkerer’ sort of characters get a chipped tooth.
In that time of insane future technology?
Even if the tech existed for everyone and was free of charge, not everyone would try and “perfect” themselves with surgery. Cosmetic or otherwise.
Fixing a broken tooth is not trying to achieve perfection.
Apparently to you it is since you cant seem to fathom the idea of someone not bothering to get it fixed.
They took the constructive criticism from the promo image of venture and fixed venture’s teeth to match the concept art. Went from simpsons teeth, to overwatch teeth.
Seems personal to you. Fix your teeth.
She probably fell or got injured while spelunking and chipped her tooth in the process.
As stated, they probably just don’t care.
I also have some screwed up teeth, but it’d take a lot of appointments and pain to properly fix everything. So I go by the logic of “Eh, as long as it doesn’t hurt, I ain’t fixing it.” They’re probably the same.
Not everyone is that worried about vanity issues. Especially for people like Venture of myself where we don’t have a career that depends on our smile being perfect. They’re digging up rocks, not presenting the 6 o’clock news. 
Now, on the actual reason why their teeth are messed up… lol It’s just a character design quirk. They’re a bit eccentric and probably chipped a tooth in the field. The not getting it fixed thing shows they have other priorities. You see this character arc a lot, like with Hange from Attack on Titan - she forgets to bathe regularly.
So it’s just a character trope. Now, we could go on about whether visual oddities are good or bad for practical game character design for days. But this is probably the writer’s reasoning.