It's a free country -- so if you want to move your money you can just do it whenever you feel like it, right?
You can certainly change banks if you want, but it's hard to pull it off painlessly. As a result, many just stick with the same bank, even if they'd rather leave for better fees and services.
Sarah Gilbert, writing for Get Rich Slowly, explains Why Most of us Won't Change Banks. She points out how odd it is that online bill pay seems to be free everywhere, but other services cost money (what do the banks gain from offering you online bill pay?).
Switching banks is hard -- not only do you have to spend time on the process, you have to have extra cash on hand to complete the process without bouncing checks. In this economy, not everybody can do that.
Further reading:

