That loss affects their stock price, their future outlook, what things they choose to fund, and how much they spend on advertising and trying to recover from this PR disaster.

My wage doesn't have a cost of goods sold line item. If I take in $5b and make $5.5b in revenue, $300m is > 1/2 of my net profit

This is flawed thinking. There is no "them" with a huge salary. The people making decisions are salaried or invested employees, and their livelihood depends on the stock regardless. There isn't "one guy" that this hits, like it would with a salary, there's thousands of investors which must be appeased.

Also, it's likely many of those canceling were people who didn't use the service as much as power users, which means they're losing the cheapest to maintain customers (industry insight, no research to back this up, to be clear).

If we had boycotts and cancelations even a quarter this big across other media giants, our media would be a far better place.