I love the logic at Sony: They wish now that the PSP had dual analogue sticks, and thought about adding them to the PSPgo, but they didn't want to trip up developers who'd gotten used to developing around terrible controls.
Sony Worldwide Studios President Shuhei Yoshida told Game Informer:
We also felt - like many users - that we wish we had a second analogue on the PSP. But we are talking about the mid-life cycle of this platform, and the PSPgo is designed to be perfectly compatible with the PSP-3000 and all the games that released before that. So we had a very serious discussion about this particular subject, but we decided not to add a second analogue, and some of the developers are doing quite a nice job translating the second analogue functionality to different buttons. We didn't want to divert their efforts either.
So even though Sony knows that dual analogue sticks would make for a better control experience, they'd rather keep things basically the same so stuff stays consistently less-than-optimal across PSPs. And besides, developers have sorta figured out now how to work around the deficiencies. Mhmm.