Vendor and developer support, community size, available tutorials, etc.
Wrt community, linux-sunxi and Armbian are both in better states than the Raspberry Pi community on their forums or on Reddit, if I google for dhclient issues with the Raspberry Pi I'm gonna get nowhere fast on fixing said issues.
How is libmmal for the Raspberry Pi's camera libre by the way? The license looks to be proprietary, definitely the opposite of open.
Literally, once I got my Pi, I got a DHT22 from my arduino box and in less than 3 minutes I could read it.