The problem is that the entire ARM economy tends to have rather spotty support as a whole. There are mountains of proprietary peripherals baked into the chips, so you can't just pick and choose better supported options like you can on PCs with removable parts.

And while a chip manufacturer may make a handful of refreshes, most ARM platforms tend to only last a few years before being completely abandoned in favor of new ones. I am frankly amazed they can still get the BCM2835.