Improve infrastructure. Apparently they are trivially DDOSable by anyone renting a few servers and running git clone in a loop? That's a problem they should solve. And no, blocking by user agent is not adequate protection.
Infrastructure costs. So you'd be willing to pay more for that?
I already pay for GitHub, am fine with that and they manage. So yes.
You're not paying for the traffic load though, Microsoft does. I think it's unfair to compare a forge run by a giant and one run by a tiny company, or for that matter, self hosting users.