Why Is my Apple Music not syncing to iCloud after reset?

Music is not synced to iCloud. If you subscribe to Apple Music stream, or to iTunes Match, your music is synced across your devices through your Apple Music or iTunes Match account. If you had personal songs uploaded that were eligible to match, those would be noted in Apple Music. You can log into Apple Music and download your music again.

I believe that music only synchronizes through iCloud if you are an active subscriber to either iTunes Match or the Apple Music streaming subscription service. I could be mistaken, but I don't believe that the "Sync Library" controls for this show up in the same place as all of the controls for other types of iCloud synchronization (Photos, Contacts, Calendars, Notes, etc.).

If you just have a bunch of purchased music but are not a subscriber, the way that you get the music onto the iPhone is through manual synchronization, from a computer, to an iPhone, iPad, or iPod.

Sync your iPhone, iPad, or iPod using your computer - Apple Support