Hard to fathom how and why people think like they do but it sound like as always it is a short cut to the top in their minds. I was always amazed at employers willing to gamble on new employees who have had multiple jobs over a short period of time as I would frown upon this. I didn't know the sales people received accounts left by others and is actually a decent bonus if you stick around long enough. The way the economy is right now who would even contemplate starting a new job as it is utter madness.
It is a hard market to get good people with experience out there - cheap at least.
They have to be moved on to others, as they need service and support over time too and they often grow and need more licenses or implementations in new regions. It can be massive for a sales person.