For the past 10 years I worked for companies with NDA and exclusivity clauses in the contracts.
I can only describe what I worked on superficially, I cannot contribute to other projects because all code I produce (even off-hours) that has my name attached to it is company property.
My GitHub and BitBucket profiles are bare, save for bug reports.
Every time I get interviewed I have to explain why my résumé is not more detailed and why I don't contribute to the open source community.