I think investors get FOMO when they see other companies buying things and think "oh shit maybe I'm missing out on this great opportunity" and reactively buy something that fits the trend in their space.
The replies seem to be full of low-quality guesses, which is disappointing to see on this site (assuming they were not using sarcasm). I’ll try to do slightly better and link the actual press release and include the official statement.
Hopefully someone who has access to the C suite at Spotify can leak the actual answer here (I’m sure they will get right on that). For future reference just Google “x acquires y” if you want to attempt to get any insight about “what x planned to do with y after acquiring”.
> “We are always looking for innovative and playful ways to enhance music discovery and help artists reach new fans,” commented Jeremy Erlich, Global Head of Music, Spotify. “Heardle has proven to be a really fun way to connect millions of fans with songs they know and love and with new songs . . . and a way to compete with their friends as to who has the best musical knowledge. Since its debut, the game has quickly built a loyal following, and it aligns with our plans to deepen interactivity across the Spotify ecosystem.”
In other words, they tried to retool the tech toward an additional value proposition for both users and artists. The result failed to meet a quality bar, and therefore it was decided to axe the project.