Or maybe you work for a company that legally prohibits you from putting your stuff on Github.

Those kind of contracts are quite common in the finance world, and to a lesser extent in R&D in big enterprise tech firms (Apple, Microsoft, etc.)

That really does depend on your market and customers. I've got a github account - but it's pretty much incidental to getting new work. My track record, value delivered, personal network, etc. do that.

Speaking of the HN bubble...

Me personally, I do have projects on Github, mostly coded on rainy weekends when nothing better was happening, or when stuck on a plane/train.

I rather spend my free time after work on this one life, with family and friends than coding.

Not to mention that most corporate work is under NDA that prevent us to publish anything about it.

I disagree entirely. I put my projects on my own site. I see no reason to put then on github in any way shape or form. What will it offer to me that my site does not?

Expecting that people will put stuff on github gives an unfair advantage to rich people who can afford to spend more time doing unpaid work, among other things.

You can read more about such arguments here -> http://www.ashedryden.com/blog/the-ethics-of-unpaid-labor-an...