I have to say, I'm surprised I don't see more of this viewpoint represented in here, especially when competent and experienced programmers are very much in a seller's market.

I think there are a lot of conflict-averse engineers. Not giving them the raises they deserve (putting the onus on the engineer to negotiate for it) sends a message employee: this company is more concerned with getting a "good deal" than with valuing you as an engineer. That's a breeding ground for sentiments of zero loyalty.