It is fucked up that the fans who are transcribing do not get a cut, but it's not like they were misled to believe they would make a cut before they started doing it. The people doing that are doing it out of a passion for the music.

I'm not saying they shouldn't be paid of course they should, if it was up to me I'd say make them all rich. I just think it's a stretch to imply that Spotify is stealing anything here

The writers almost certainly do get a cut. Musixmatch does not own the copyright to any of the lyrics, and as such, negotiated with the copyright holders in order to be allowed to store, display, and sell access to the lyrics. This almost certainly involved some amount of money changing hands.

Spotify is paying money for access to the lyrics and using that as a feature in their product. A chunk of that money is almost certainly going back to the actual writers.

Spotify is receiving money for something they did not create.

Spotify are paying musixmatch for the lyrics.