If you have a look at the docs for that endpoint https://dev.twitch.tv/docs/v5/reference/streams#get-live-streams you’ll see that sortby and direction are not valid query parameters for that endpoint, which is why they didn’t change the results.
Looking at the link I’m not sure how they do it, but considering they seem to be doing a lot of work with tracking channel stats I wouldn’t be surprised if they just poll all streams (at the time of writing this there’s about 17000 live, so not too hard to poll through the pages), store the results in their own database and then use their own API which does allow for sorting that the page can use.