In good times, it's easier to find a replacement customer for an existing one in the event things don't work out. Of course, a steady stream of replacements is considered a good thing...marketing is working. Except that it makes us lazy. Why sacrifice everything to retain customers as long as there's a back-up? The obvious answer is that there won't always be one...called lean times.
It's a simple choice, work like heck to create some insurance. Or, hope to get lucky.