The simple reason is because I got a lengthy free trial for it (saving me money on the Tidal sub) and then stuck around.
Apple Music was hot garbage when I started using it but over the months of my trial it improved tremendously - to a point where there isn’t much difference between it and Tidal. App performance is good now, it provides song recommendations for your playlists, many bugs I was facing have been fixed.
The Android Auto experience is better for me compared to Tidal, it has Shazam integration (Spotify does too, Tidal doesn’t) and it has many of the Japanese city pop songs I like that Tidal was missing.
I can always jump ship if needed. Services like Soundiiz and TuneMyMusic make it pretty easy.