My bet is that since trending likes are a Graph DB problem, SoundCloud just chose not to solve it once it became too hard on their database. They famously had issues with early Mongo adoption so this would fit right in. Their most recent frontend HTML5 rewrite always winds up my CPU and hasn't changed in a couple years.
SoundCloud to me has always been a great idea with some great design that got ruined by some poor engineering choices from the top. And at the end by a desperate grab for stats and cash. I think producers would have paid more, better subsidizing free plans, if discovery hadn't gone downhill. I ran the numbers once on how CDbaby and Bandcamp became successful (based on stats trickled out over the years) while SoundCloud could never turn a profit. There's still plenty of room for someone to do this right.