Well, my teacher told me it was because the cream is less dense than the skim milk it floats upon. It seems we have an analogous situation with wealth in our society.
Like the cream in a milk bottle, so  much of it has risen to the top, only the top in this case is  the 1% who have accumulated  vast amounts of wealth in the past seven years..  It's funny that Karl Marx predicted this back in 1848 when he lived in London and personally witnessed the social upheaval that was the industrial revolution.
I think of him as a dutch uncle,  only he was German and edited a major newspaper when he was twenty-four years old.

The reactionary politics in Europe drove him to the haven of England where he saw the effects of rampant, unfettered capitalism.