Neither are trapped, either is experienced enough to know what was coming. Money talks, Alonso signed one of the biggest deals on the grid. No one, absolutely no one with any sense see's rushing a complex piece of engineering as smart. They both signed new deals with Mclaren for money.
Ron's arrogance could easily have made him believe they might be competitive this year, even Ron probably realises they won't be competitive next year either now. Considering the lost sponsorship, the incoming loss of constructors money even though Honda appear to be covering half the wages(of Alonso or both, not entirely clear) it would save them a bunch of money to release both and have Mag/Van in the car at a fraction of the wages, would save them and Honda probably £30-35million next year.
Massa is apparently only in the 3-5mil income range, Button apparently on 8 going to 12m for next year, Alonso supposedly on 25-35mil(often quoted in € so maybe £25mil), these are amounts no other team can come remotely close to offering them.