I'd add the move from feature phones to smart phones and later tablets. Early adopters were getting them 2007/08, 5 years on from that the platform was well on its way to maturing and with a broader range of hardware and the software ecosystem was moving to target it too. Then there's the question of what form best suits the usage the tasks the netbook audience have, if you're doing the very basic browsing/comms tasks, why take a comparatively big slab when a 4-5" will do, and if you do need a portable PC why constrain yourself to a weak system, netbooks were in no-mans-land.