When it was publicly announced that McLaren had signed Alonso, Montoya saw the writing on the wall, that he was on the way out. And it's no secret he's been shopping with other teams. But I think his options within f1 were limited. He most probably only wanted to go to a competitive team, and that's where he didn't get and offers that were acceptable.
And who are the teams considered competitive? The ones that have a realistic chance of running up front? Ferrari? It all depends on Shu, if he stays, he definitely won't go along with a teammate who does anything but support him. In fact, Massa may be on the way out of Ferrari, He did too well at Indy. And Kimi most likely is slated to fill Shu's seat, once he leaves. So Montoya to Ferrari seems improbable, we're just not going to see him as Michael's bitch, or as a teammate to Kimi again.
Renault havee some kind of driver plan in place, with Fisi in one seat, and Kimi or Heikki in the other.
Both Honda and Williams appear to be satisfied with the current driver stable, and won't change drivers. And Toyoya must be smarting from the Ralf experience, paying so much money for a driver with a spotty record, a few wins, but no sign that they will ever improve, or even be able to put forward 100% each and every race.
So to me, it appears none of the big teams have any interest in Montoya at this time.
So Montoya talks to his old buddy Ginassi, and a deal is made. Ginasssi could use a big name driver, and if he swings to Toyota next season, it's all good stuff. Montoya gets to live in Miami closer to his family, and in a culture closer to his heart. He will get to race almost each weekend, in a moch higher level of intensity and competiveness. And don't forget just a few years ago he and Jeff Gordon swapped cars for one day at Indy, on a pr exercise. So he has a basic understanding of what a stock car is.
JPM has a lot of fans in the USA, from his CART days. Going back to there will re-energize that fan base, and he will make millions selling T-shirts and such to the fans.