Of course, you're right; each individual photog has the power to tell the Times to take this contract, fold it till it's all sharp corners, and jam it (and some have done so). And he or she has the right to take the contract and sign it also (and some have done so).
The reason is rather simple: there is a large supply of photographers who seek a Times credit, and so the Times can be high-handed. Having Times credits helps a photographer seek other assignments. So mostly the guys who sign will be young guys trying to break in, and guys who have unwisely let the Times represent too much of their income. Most of the name photographers will probably tell the Times to pound sand.
The Globe photographers banded together and sued (in front of corrupt Massachusetts judges, they were wasting their time, but that's what they did). The Globe contract is unprecedented because it even gives the Globe ownership of stuff the photog shot before signing the contract.
IANAL, but I don't think that what the Times and Globe have done is in any way illegal. I think it's unethical to the max, and it's hypocritical, although typically limo-liberal, to mistreat the 'help' like this.
d.o.l.
Criminal Number 18F