I learned this way back in the early internets when some photo storage service (I forget which) suddenly shut down.
Amazon Music will end its streaming support for users' uploaded MP3 in 2019, the service announced this week with a statement on its website.
Amazon Music Storage subscription plans, which let users upload music from their Mac or PC and stream them alongside the in-app on-demand and radio options, will be accepted until Jan. 15, 2018. Then, the service will run until January 2019, when it will be removed entirely.
Good for temporary storage and flexibility, so you can access your stuff from multiple locations. Not a long term option. This isn't some startup. It's Amazon.