The GameBoy Micro is not the best form factor. Actually the original GBA was the best form factor (never played on SP but it looks like a hand cramp). Try playing Street Fighter Alpha 2, F-Zero, or Mario Kart on a GameBoy Micro. It becomes a hand cramp very quickly especially if you have decent size hands. I have 20th Anniversary Famicom Edition GameBoy Micro and I'm proud of it but it's only good for games like Advance Wars. I see you put usually there but I still had to bitch about controls. The original 3DS was crampy also with MK after a decent session along with dare I say the phat DS (fuck snakers in MK DS).
It's not universal no. But on the other hand, late gen revisions are for diversifying usually, appealing to those who haven't bought in. For some, the super small Micro was attractive due to the discretion of it.