Sometimes developers don't have a choice about putting their work online--many large companies actively discourage (or prohibit) their engineers from participating in any meaningful way in open source projects.

Want to post your personal hacking online under your real name? Nope, sorry--"everything you do belongs to the company, and we can't take the chance that you might accidentally post some uber-valuable trade secret." So rather than risk losing the job, you just find some other, not-publicly-visible way to spend your time.

Maybe this group of developers isn't viewed as interesting to many employers, and if that's the case my argument isn't worth much.