Most bounty programs won't pay for DoS at all.
Every application has a bug that can bring the whole application down for every user without owning a botnet? That comes often with a significant business cost, if someone exploits it. Many companies take them seriously. I have reported many as high and business has agreed. Not with HackerOne thought. If there is a bug where someone can make your whole product down with a single laptop isn't really something you can just ignore.
Which can be definitely high, if it can be triggered by giving specific URL, for example.
I think there is too much generalization happening here.