Why? Apple does a great job on photo saving. What am I missing?

Space is cheap for them. They get heads up on all the sales...
But seriously, the more data any company can get from a paying customer, the easier they keep said customer.
The app may be free but prime is not.
Wait, is prime required?

AAPL buys cloud services from Jeff Bozo and resells it to you.

I don’t pay for storage or Cloud. Just keep minimum which is fine for a little ole lady.

App is free. You get 5GB of free photo & video storage if you are not a Prime member. Prime members get unlimited photo storage for free (plus 5 GB of video). Integrates with Fire/Echo/Android devices for photo sharing/slideshows/screensavers. If you don't have Prime and/or those devices it's probably not gonna appeal to you too much. If you already pay for Prime, you can use for unlimited photo storage rather than pay for it somewhere else. If you have a variety of Apple/Amazon/Android devices, easy photo sharing between them all. As always, YMMV

Quote
MEG
App is free. You get 5GB of free photo & video storage if you are not a Prime member. Prime members get unlimited photo storage for free (plus 5 GB of video). Integrates with Fire/Echo/Android devices for photo sharing/slideshows/screensavers. If you don't have Prime and/or those devices it's probably not gonna appeal to you too much. If you already pay for Prime, you can use for unlimited photo storage rather than pay for it somewhere else. If you have a variety of Apple/Amazon/Android devices, easy photo sharing between them all. As always, YMMV

I pushed it and uploaded 1 and a half Terabytes of RAW files for the heck of it. It took forever to upload, but it did it. You have to tell your devices to turn off video uploading because they'll nag you to buy more space.