There is a psychological aspect too. Show people 10 results and they'll actually look at them. Show people 100 results and they'll not only quickly scroll throu

There is a psychological aspect too. Show people 10 results and they'll actually look at them. Show people 100 results and they'll not only quickly scroll through them but also skip the top results, which is counterproductive. The big sites have definitely AB tested changing the results per page and have stuck with 10 for some user metric driven reason.