Witness the latest Target breach. Millions stopped shopping there and Target was (rightfully) forced to take numerous steps to draw people back in.
Because there are alternatives for shopping. I have exactly 1 choice for high-speed Internet, Time Warner Cable. When they roll out their tiered Internet and I don't like it, what do you propose I do?
A grocery store near where I lived stopped carrying a lot of things I liked to buy. So I stopped shopping there.
And if they were the only grocery store, you'd just cheerfully starve, right?
Basically any company that has customers, is accountable and will self-regulate based on customer feedback.
And when you grow up, you'll realize that this little theory only works if the customers have alternatives.
If you'd like an example: text messaging: It uses some empty space during the messages that a GSM phone has to send to the tower anyway. It costs the phone company virtually nothing (just the routing servers, which aren't pricey). Yet there are zero cell providers in the US that offer really "free" text messaging. All of them require paying more than "voice only" plans.
How about baggage fees on airlines? With every airline other than Southwest charging them, customers actually don't have alternatives.
And that doesn't even get into the situations where nominal competitors directly collude to screw over customers.