I've never worked for a company with more than 30 employees or so, or on a team larger than 4... so it may be that the self-effacing people I'm describing tend to show up in smaller organizations. Or it may be that small teams bring out a side of people that's more willing to share the glory and shoulder the blame.

I've certainly worked with the type of people you're describing, but they stand out like a sore thumb in a smaller work environment. Their ego becomes a subject of contempt.

And also, just on a human level, there are many of us who don't aspire to glory. It might be as simple as having an internal sense of pride in knowing you did a job well, even if no one will ever know that you were the one who did it. I have a lot of friends who fit that description, who simply enjoy tinkering and building things and want little to do with the rest of the world. They make great employees for companies, but they're often overlooked because they don't promote themselves.