I have no idea what Triplebyte gets or even what their business model is, but typical recruitment companies get a lot more than that -- on the order of 15-20% of the first year's salary, so on the order of $15-25k. I suspect Triplebyte is less than that, but could be an order of magnitude more than you've guessed.

When I last used headhunters they charged 20-30% of a years salary. So they are likely making $25-50k each. So that could be as high as $25-50M