Why does Japan waste so much IT talent? The shortage of Japanese software engineers for tech startups has long been a puzzle in a land of 4G telecom networks and pioneering mobile social networking.

Excessive regulation, excessive modesty and excessively cautious moms were among the slew of explanations offered Tuesday by some of Silicon Valley's hottest names at a Tokyo forum organized by Internet billionaire Hiroshi Mikitani's new lobby group.

Mr. Mikitani is chief executive of Japan's biggest Web-based retailer Rakuten and a leading figure on Prime Minister Shinzo Abe's advisory panel on improving Japan's competitiveness. Mr. Abe's pledges to deregulate Japan's regimented economy helped inspire a mood of optimism at the forum.

Among the keynote speakers looking to bring some entrepreneurial disruptiveness to Japan's Old Guard at the New Economy Summit were Google Senior Vice President Andy Rubin and Twitter and Square co-founder Jack Dorsey.

The reasons cited for Japan's surprisingly low number of software engineers willing to embrace the challenges of working for new IT ventures included the following: