I will say it again for the thousandth time. The most likely consideration is this. Microsoft traded its production rights for the PC installment of the game to Electronic Arts in exchange for continued exclusivity of this series. That may not seem important to most of you, but for Electronic Arts it was twenty to thirty million dollars of pure profit at least.
At the time given what Electronic Arts had just spent, and Mass Effect being the least of what they acquired. Well it probably would not have seemed like such a loss. Yes it would have been expensive for Microsoft, but that is money that doesn't disappear from a balance sheet. Hell the fact that Microsoft has not sold the rights to the first game back to Electronic Arts only highlights their intentions.
The sequel being on the PS3 is very much a pipe dream. Microsoft has too many inroads in the series. Contracts in place before the sale. Contracts after the sale. They probably even have certain proprietary rights. Microsoft didn't blow a bundle of cash to see Sony get its hands on the trilogy. The same way Sony got leveraged into paying out the ass for Metal Gear Solid 4.











