Remember that timely payments are also a factor. If they laid off their personal assistant who's been making all of their payments and they haven't bothered with the mail since....
Just kidding; but that's probably happening somewhere 
@Anonymous-own-fico wrote:Can you be in the 600s and not have a derogatory? I'm not sure. So that could explain it. And of course, wealthy people, not needing credit like the rest of us do, may well have better things to do than meticulously zeroing cards before the statement date! A variation of such a correlation is that the scores of some people who have a vast knowledge of credit are in the 600s; the forums here have plenty of them on display on a daily basis. What's going on?
Yes you can be in the 600s without any derogs on file. High util will easily do it
Income, of course, has nothing directly to do with credit scores. But it does have an effect. High income makes it easier to get both high and, oddly, low scores.
It makes high scores easier because generally one has enough money to pay the bills. You are not looking around to decide which Peter to rob to pay Paul.
But high income also makes it easier to have low scores as well. It's pretty easy to live off debit cards and cash. It's also easy to let bills slide like utilites you didn't close when you move or parking tickets that went to collections. Sure you get phone calls or dunning letter but they are annoyances. Since you aren't using credit you have no idea your scores are in the tank. You really only find out when for some reason you need credit and when your income is high enough those reasons occur much less frequently.
So high income enables you to be a bill paying flake. Been there, done that before I reformed. I don't recommend being a flake.