It's because it was originally developed for smartphones: originally normally trieted as devices, then adding the ability to act as hosts, therefore you have a

It's because it was originally developed for smartphones: originally normally trieted as devices, then adding the ability to act as hosts, therefore you have a USB host "on the go". The more modern version and terminology is USB-C dual-role support, which is the same basic thing but using the USB-PD protocol to negotiate instead of a special marker cable (which the product page does also use).