It might have been nice of them to change the name slightly to avoid confusion with the originating FreeRTOS. https://www.freertos.org/
> The FreeRTOS kernel is now an AWS open source project, and these pages are being updated accordingly.
Given that, the distinction probably isn't super important.
Most likely Amazon's motivation is that they can make sure FreeRTOS makes using Amazon's services very easy; there are some IoT offerings that can't connect to Amazon's services, (or at least can't connect easily) [2]
By making sure FreeRTOS can easily pull in the right libraries, they can make it easier for people to connect devices to AWS without compromising on secure encryption.
[1] https://aws.amazon.com/blogs/opensource/announcing-freertos-... [2] Last time I checked, Amazons MQTT service required TLS1.2 and an esp8266 only supported TLS1.1