I'd say it's a feedback loop. The top AAA developers (particularly western ones) tend to want to push graphical and technical boundaries with their games (not so much gameplay), so all the less experienced, not as talented devs are put on the Wii games, which end up being bad games, which don't sell well unless they're casual, which just reinforces the notion that the Wii is not a platform they want to work on. I wouldn't say they were morons or necessarily doing it deliberately (why would you want to sabotage something that has the potential for insane sales?), but lack of leadership and a mindset focused on technical advancement over new gameplay probably has a role.
Regarding PSP, you would still be hard-pressed to call the ports AAA games, and the control schemes are fairly similar to the HD consoles'. Why would you want a dumbed-down port on the Wii anyway?
Currently playing: Gran Turismo 5
Just finished: Infamous 2
