What disturbs me is that he appears to have one knee further over than the other. A little over at the knee doesn't bother me too much if he has a lot else going for him, but uneven conformational faults like this send a red flag to me.
I don't judge babies for being over at the knee as it can often turn normal or near normal as they grow. Unlike back at the knee which will stay.
But to answer your question, people are greedy. People will breed HYPP positive horses so long as people pay the breeding fee still.