I'm a prime member, have been for a while. I just tried to import my library, it said I had 250 songs I could import for free. It then asked me if I'd like to pay $25 to upgrade so I can import any number of songs. I was able to upload all my songs to google for free.

Dang. Didn't realize that Amazon charged you past a certain number of songs. I have my whole library uploaded to Google as well. I usually use spotify, but it comes in handy sometimes (like when I want to listen to the Beatles).

What is the point of uploading music I own to a cloud service so I can stream it later, wasting my precious mobile data? My phone has gigabytes of storage and I can transfer thousands of tracks in seconds.

Convenience. I have like 150 gigabytes of music. I can't put all of that on my phone and even if I just put a subset on there I'd have to re-load it every time I get a new phone. What if I want to play the music out of whatever laptop or tablet I happen to be using at the time? Also, I don't have to worry about my hard drive dying. Also, Google lets you save the music to your phone so you don't have to use mobile data.