Generally market bubbles come to an end when you run out of fools, but in this case the supply of fools seems just limitless. What’s the story here? Where are

Generally market bubbles come to an end when you run out of fools, but in this case the supply of fools seems just limitless. What’s the story here? Where are they coming from? Is it massive leverage? Is it free money from the fed? What accounts for the endless supply of idiots? I really do want to know who is buying at these prices and where they are getting the cash to do so.