Apple Music for Android is not about Android users who want to buy Apple Music. If you have a family with mixed iPhone and Android devices, if you can’t use Apple Music with all of your devices, you will probably use Spotify. I’m sure Apple is glad to take money from Android users who want to buy Apple Music, but there are relatively few people who fall in that category.

iCloud/iTunes is available for Windows because most people who have iPhones (and iPods before) have Windows.

There is no financial reason for Apple to make iMessage for Android.