With the money they raised, after spending so much on marketing, I assume they downsized, lost some talent, and pivoted mostly to a sales-driven recruiting business for their top clients.
And even if they stayed to their original model it would have been too easy for niche competitors to erode their margins. Think Triplebyte for Android developers only times 20 different programming areas.
I can't imagine the difficulty to accurately measure the success or failure of long-tail HR hiring processes like phone screens. The success or failure of a candidate post-hire has so many variables it must be very hard to attribute them to signals present in a screen. I imagine most of the data points are derived from signals found in successful candidates, and then trying to find them in an assessment or screen.
Its really hard, and I hope the negative tone of my comment does not suggest I don't respect the problemset and the people willing to throw themselves at it.