Nor have I. As a manager/co-owner I can't think of a reasonable business-friendly way to allow my developers to spend work time on OSS. I would love to, of course, but our systems really do not facilitate community involvement.
It's one thing to write the code, but another thing to publish as open source. There's overhead: coordinating the PR in an existing project, responding to issues, writing a decent README, looking at PRs, etc in your own.
If you spent 1/10 of an engineer on an open source product, and 100 other companies do the same, your company gets much more than it puts in. And because it's open source, you know how to fix it, and you can fix it.
I know of multiple billion-dollar companies who can't get the time of day from Cisco, HP, etc. for bug fixes or new features.
The vendors attitude is: Bought 10M of product in the past year? Meh... piss off. We're working on important customers.