Because it is very good cooked more quickly and served medium rare in thin slices.
I always have had good luck making a pot roast out of bottom round.
Linda C

I don't get what you are saying...a pot roast if NOT cooked to medium rare. It's cooked all the way through. A roast beef is cooked to different degrees of temps, but NOT a pot roast. How do you make a medium rare pot roast??

A bottom round must be cooked either fairly rare and sliced thin, or braised....but not cooked very long, as it's a lean piece of meat and will get stringy if over cooked, even in a moist enviornment.
Linda C