1a) My reasoning is that the Wii wasn't cheaper to develop for as a small developer if you had to hire a whole new team, or train an existing one from scratch to work on the Wii hardware and create a whole new engine. And then you also took the chance that either the majority of the Wii audience wouldn't like your game, or the hardware wouldn't let you do what you wanted to do, or there was already a Nintendo game that owned your category.
On the other hand, you could just keep doing what your team knew how to do (PC/PS3/360), fully make the game you wanted to make, and triple the chance of recouping your costs by releasing it across three platforms with a minimum of additional time investment (PC to 360 would be easy, leaving the majority of porting effort to be put into PS3). Even better, you could add DLC into the mix post-launch and then double-dip with a Game of the Year Edition. None of this was possible on Wii.
1b) As for the similar architecture, that does make it easier...if you already have people on-board that have used that architecture. A lot of the third-party developers that have risen to prominence since the 2000s are coming from the PC world, not the console world. Bethesda, Bungie, Epic, Rockstar, Infinity Ward, they all started as PC developers with no GameCube experience at all. The ease of porting to 360 was what got them involved in the console space, and they were making more adult-oriented games to begin with, so they never deviated from that or felt a need to make something more "suited" to a Nintendo console.
2) I don't know. Maybe they hired the B-Team, which is entirely possible. Just because something is exclusive doesn't mean it's going to be good.
