Exactly this. They're not great, but there's something about being a customer somewhere for a very long time that genuinely does (or did) seem to offer you a mortgage rate that was advantageous.
In general, banks compete on other attributes - a small difference in a mortgage interest rate is a lot of money and makes up for a HUGE difference in the quality of internet services; and whenever loan market becomes tight (and thus it's not attractive to refinance to another bank) people are pretty much locked in.
