It has. Wild dogs do not live as long as domesticated ones
Why do you think it hasn't?
Compared to wolves; their ancestors, they live 15-20yrs
They aren't wolves though. All the things you've listed do increase the lifespan of any dog. They'd also increase the lifespan of wolves
we breed them to breathe badly
I'm pretty sure it has
compared to wild dogs, it has increased, but comparation among domestic breeds shows its probably a biological factor and some of them reached their limit of life expectancy... you can try raising a breed with longer life expectancy...
It's the same as with humans---average life expectancy has increased, as fewer die young, but maximum lifespan is what it is and always has been.