This is happening on Apple Music for Mac as well. It's a mind-boggling omission - or "bug" if you will.
This might not be such a big deal to many, but for certain genres of music, it makes the Apple Music experience almost unusable.
Take classical music for example. The composer info is the only way to identify most classical pieces of music. The artist is just the musician / orchestra / ensemble playing the music. If you have two symphonies by two composers on the same album for example, the only way to know what you are listening to is to look up the composer. Yet, on Apple Music you cannot do that. And yes, shockingly on the iTunes store all that info is available, as it should be.
By the way, Spotify always lists composers for classical music.
And yes, I have sent feedback to Apple as well.