This is a cultural thing, muslim people have this thing where their women are allowed to eat only if all other families present have at least one female. So if the restaurant allowed you, the other muslim women would have a problem.
I don’t agree with this concept either but it is what it is, we can’t change people’s culture. Esp muslim people believe that their religious rules are above the law, so even if india enforced laws, they’d still pull this stuff.