If I read one more opinion piece lamenting the death of consumer loyalty, I'm going to wig out. This is one of those questions where the answer is as plain as the nose on your face, so I wish everyone would stop treating it like a big mystery. Marketing groups at many larger corporations are typically split into two areas - acquisition and retention. While the acquisition group tends to get the majority of the emphasis (new customer growth seems to be sexier than retaining existing ones), retention is typically underfunded and de-emphasized. It almost goes without saying that when your bank, automobile manufacturer, cellular provider, etc. starts taking you for granted, there's little incentive to stay with them. In many cases, the only force keeping you with them is inertia.
It's completely weird to me that a bank would wonder why their existing customers are switching to other banks when they're giving better deals and incentives to new customers while doing diddley squat for their existing customers. Why would I keep a checking account that charges me monthly service fees when the bank down the street is running a "free checking for life" promotion that gives me a $100 gift certificate to boot? See enough of those customer acquisition promotions and you begin to wonder - "What has my bank done for me lately?"
Lots of corporations wonder why their existing customers are defecting. It's because their competitors are offering better deals, and often because the company itself is treating its new customers way better than customers that have been with them for years. This totally flies in the face of Marketing 101, where one of the first lessons you learn is that it's much easier and less expensive to earn more revenue from existing customers than it is to launch an effort to acquire new ones.
So count me among the folks who wander from company to company, looking for the best deal du jour. And quit acting like the sky is falling because the economics of the very situation you created make it easier to switch than to hang on.