Since people can transfer wealth between generations, this seems inevitable. A college education is a good thing, but it's hardly surprising that it doesn't compete with what comes with a parent in the top quintile.
This reminds me of a quote from The Heist: "Everybody needs money. That's why they call it money."
I'm actually surprised that more than 41% that start in the top quintile can't stay there. Perhaps more interesting would be to look at 10% divisions rather than 20%. Making more than 80% of the country is nothing like making more than 99% of the country.