real estate billionaires

[Kevin Humphreys]

I have read some excellent posts from @Brandon Turner  (and others) on building one's real estate portfolio incrementally and how the math works.  It all makes great sense.

My question is this--how did billionaires who made their fortunes in real estate (like Sam Zell, just to pick a name) make so much money solely through real estate?  Brandon's posts describe the piece by piece process of building a real estate portfolio.  Seems like it would take a long time to become a billionaire this way.

I apologize if there is a better BP forum for posting this question.

Thanks!

Kevin