I have been both an IC and a manager, and when I was an IC I saw managers as vampires who fed on the blood of ICs. When I was a manager, I saw ICs as a bunch of whiny, entitled cogs. I am exaggerating for illustrative purposes.

Perhaps the manager had not been informed before of the IC's financial demands; perhaps the manager could not offer a raise before the employee had received an outside offer because of company policies; perhaps the manager did not see the IC as particularly capable, but this offer from a solid company made them think they had made a mistake; or perhaps they thought it was a bluff, and now they are paying for the all-in.

It is good to be cynical and to have one's own self-interest in mind. But the caricature that sees management as incompetent, corrupt or vindictive is all too easy to present to an audience that is well receptive to these appeals. I have met many like those, sure, but I have also met many ICs for whom I could use the same adjectives.