because “existing companies are more likely to miss new opportunities”
or to quote from The Economist leader on November 22 (2008) All you need is cash :
One reason why downturns tend to be good times to launch new businesses is because established companies abandon promising growth opportunities too fast. Oracle and Microsoft were both born in difficult economic times.
See also Don Dodge at Startup Empire: Starting a Company in Difficult Times and Howard Lindzon at Startup Empire: Why Now is a Good Time to Start Your Startup