Gundato: I can't speak for the others, but OFP might have been licensing issues. Bohemia Interactive made the game, Codemasters published it. BiS and Codemasters aren't exactly friends these days, so it is quite possible that OFP got pulled because it was unclear who should get what percentage of the profits.
Stiler: CM owns the righits to OFP and it's name.
BIA has moved on to the ARMA series now.
Yes, but the problem is other things Codemasters have done (claiming that OFP2 was made by the same people who made OFP1, calling it the true sequel) that probably resulted in BiS threatening to call them on some of the grey areas of the contracts. Either way, it is likely unclear as to who gets what percentage of profits, and Codemasters (and BiS) probably felt it was easier to just not have OFP be sold (and thus, make us all get OFP2 or ArmA).