"No, I WON'T stop to Google 'combustion' for you!"
A Distributed Denial of Service (DDoS) attack is when multiple sources overload a target computer with requests to prevent it from getting anything done. The Duh-DoS is the organic equivalent, with multiple people asking duh-worthy questions. If the target answers, they're wasting their energy on someone with no intention of listening. If they don't answer, they're accused of admitting there's no real problem. No matter what they do they're at a disadvantage, which is exactly the problem they were fighting in the first place.
It works on more infernal and shittier levels than a Malebolgian leak. It resets every discussion (imagine a basketball forum demanding that the concept of points be re-explained at the start of every thread). It automatically devalues the woman's experience, because her statement that she experienced sexism is invalidated by implication: She must provide external proof. It also elevates the questioner to the position of authority, the ultimate judge who must be satisfied before he'll deign to consider the problem. As opposed to an asshole rando begging for the block button.