Source: Fox yells at people to help her cub stuck in drain, but he’s too deep for them to reach alone
It’s what happens when animals are born who are not afraid of humans, and when being comfortable around humans improves their chances of survival and reproduction.
I expect that mother and cub have people who feed them, and may even pet them. In a few fox generations we may well have pet foxes who live with a human on a voluntary basis. If we don’t have them already.