Wouldn’t the solution be to just start charging for excessive DNS traffic?

Potentially yes, but that's a business decision which the on-call developer cannot deal make on behalf of the business.

There's a lot of stuff the dev team can do that are not strictly business decisions though. Rate limits, QoS, etc.

Those can be business decisions too though. It depends on whether or not the real / lucrative customers will notice, or maybe the noisy customers who will be all over twitter because a dev figured they'd make a big change like this on their own.

Throttling and tiering can definitely affect more people than you might suspect (like spiky services) and considering data and use are important.