[7dare]

I don't get why Amazon would get control of the entire TLD. Can't these new TLDs be managed by some other entity which hands out domains to those that want them?

[icebraining]

Amazon got it under ICANN's New gTLD program. There have been over 1200 TLDs allocated: https://icannwiki.org/New_gTLD_Program

[mejari]

This is How, not Why

[Kalium]

The "Why" is because Amazon decided to keep the gTLD for itself, rather than act as a registrar.

The document linked by grandparent also goes into the historical background of how this process came to pass.