Why doesn't Spotify support .m4a files?

[NpXX]

Plan

Premium

Country

 USA

Device

(iPhone XS Max)

Operating System

(iOS 12)

My Question or Issue

I'm trying to migrate music from my iTunes library on my Mac to my new iPhone and  I'm confused why Spotify doesn't allow .m4a files to play when migrated or include the album artwork from those song files too.

It's pathetic for them to expect us to use files that have less quality audio and seemingly punish you for not doing it by making songs unplayable when they fall into that criteria.