My own The Greatest Speculation of All regarding this very subject:
Sony had the exclusive F1 licence from 2003-2007 (this is the only accurate information and starting point of this theory).
Bernie Ecclestone was unhappy with the revenues and market-shrinkage due to not-so-well sales of PS3 and huge limitations of profit from sales due to "exclusivity". His guys at FIA also advised him not to sell the licence for next seasons to Microsoft, since it would again be "platform-exclusive".
And notice that this F1 season is the most intresting in last 10 years, while next one could even surpase this one. Not having a official F1 game for this and next season is just burning-your-own-house.
FIA made a secret approach to major multi-platform publishers with enough cash to pay licence fee. At the end Activision got the preliminary rights to F1 games-licence, but with obligation to find succesful developer with great recognition that can push the F1 game sales to old-times fame. From 1996 to 2001 F1 games were pretty much AAA-sales titles. Bizzare own "Formula 1" (1996) was the best-selling game in Europe and 2nd best-seling game WORLDWIDE for that year. It was surpased ONLY by Final Fantasy VII.
Activision then approached Bizzare (developers of legendary F1 games in times of PSone - Formula 1, Formula 1 '97) to make a F1 game for multiplatform next-gen. Bizzare just said: Hell, yes!
Also to back up my theory - this is an excerpt from Bizzare official web regarding the moment they handed the F1 development to another team (which was decision made by publisher Psygnosys) after finishing the Formula 1 '97 game:
"And then we handed the Formula 1 series back to Psygnosis, where they have taken it forward with F1 98 (Visual Sciences) and F1 99 and F1 2000 (Studio 33). But it was with a touch of sadness that we move away from Formula 1 games, at least for the near future. Perhaps we'll return to them one day..."
Maybe that day is closer then we think.
Official press-release from Bizzare regarding move to Activison could also be a move to my point:
"Let's talk games then... that's why we're all here after all. Well, we're no longer tied to just one platform for starters. Our future titles can be on whatever we please - we are a truly multiplatform studio now. Of course that doesn't mean that we'll be forced to make a port of every game to every console in existence... we simply have that option available to us.
Both of our two main game teams are about to start work on two new AAA titles for Activision. One will be a racing game, and the other a character game. Of course we'll make some more detailed announcements in the future, but be prepared for something big and exciting!"