It's quite the contrary.
Japan, or at least its entertainment industry and pop culture, is full of entire franchises started by minor, independent artists and coders, aka doujins [0]:
> amateur self-published works, including manga, novels, fan guides, art collections, music and video games. ... Of the $1.65 billion of the Otaku industry in 2007, doujin sales made up 48% ($792 million).
You forgot to mention it's mostly because doujin is pornographic in nature. That's why it's so big. Now if you were to classify pornography in a separate category, well the numbers would look much lower.
Many visual novels too, though they may include sex, aren't really focused on porn, just like the many Hollywood movies that contain sex scenes are not "porn."
https://news.ycombinator.com/item?id=14400642 http://www.kalzumeus.com/2014/11/07/doing-business-in-japan/
WHY is even a physical Silicon Valley still necessary?
One could argue that the doujin way is a better launchpad for a wide variety of ideas than VC-funded startups:
People, especially young people including many females, create something from the comfort of their bedrooms, without any pressure (like many software/game devs of the 1980s), other people enjoy and even improve their products, and if they get popular enough then big companies may turn them into proper franchises.
Why doesn't the US foster that kind of environment more? Why does everything have to be a company with millions of dollars? In fact, most of the Western internet is actually hostile to young artists and developers..
More than...what, exactly? Vastly more people do what the startup scene dismisses as "lifestyle" small businesses than VC-funded startups.
How do we recreate the bedroom coder and garage inventor culture of the 80s that got this industry and world here in the first place?
We don't even have devices that you can code on out-of-the-box, anymore...