Unicorns used to be a rare breed. Not anymore.  When Aileen Lee of Cowboy Ventures first coined the term “unicorn” — referring to startups worth $1 billion or more — in 2013, she identified 39 unicorns. The vast majority were valued below $5 billion. Apart from Facebook, the average was $3.6 billion. And 27 of them were based in the San Francisco Bay Area. What a difference eight years makes! 2021 has…