1. Because I know they will more likely make it for all platforms. PC is my choice to play it on.
2. The focus has always been on multiplayer and would like that to continue as the series goes on.
Free Radical second.
What they did in the trailer looked great. I hope the new one has the look and feel of what they were doing but it did worry me to see lots of time spent on a single player aspect of the game and no shots of multiplayer action.
No, most of what I see them adding in the expansions are not all that great, I fear they would slow the progress down if they had the series.