I don't know why submitting a vulnerability on those platforms is still free. If reporters had to pay a little amount of money (let's say, 20-50$, or indexed to the maximum gain of a vulnerability in a given category) when submitting their report, maybe those would be of better quality.

I know that this poses new problems (some people can't afford to spend this money), but it would be better than just wasting people's time.

This point is brought up and discussed in the linked article.