Apple Music/iTunes

'This computer is already associated with an Apple ID. If you use iTunes Match with your Apple ID, you cannot use iTunes Match, auto-download or download past purchases with a different Apple ID for 90 days.'

How can the computer itself be associated with an Apple ID? There are multiple family users on the MacBook Air, switching all the time. But once my partner, for example, has used iTunes/Apple Music on the MacBook Air, I cannot play music that I have downloaded from CDs or retailers' download links on my own Apple Music account until 90 days later. It makes no sense that the whole device is associated with an Apple ID and Music Library, rather than the user account being associated. It make Apple Music unworkable and means that it's simply a lie to state, as Apple does, that by paying a subscription you can play your music on all your devices/accounts. It's dishonest and the rule appears to serve no purpose, so why not get rid of it. Apple doesn't think we are all going to buy new MacBooks just so that we can use the AppleMusic app, does it? There are other music apps that don't limit their use to one user per device. It's nuts that Apple hasn't fixed this. Can the next MacOS upgrade please associate Apple Music with users not devices?