I think UI is actually the biggest issue. Currently, it's faster to search and play a song on Spotify than on Apple Music.
Completely agree. They have lossless music, people who started their iTunes libraries since the iPod times, all the iPhone users. All they need to do is to make Music App look great, user friendly and bug free.
People want to see their music library with the gorgeous cover art, press play and enjoy the music. "That's it. It's so simple"
That's what made the very first iPod so successful. It was easy to find your songs and play them. Especially in comparison with other players that existed back then.