[indigochill]

Another reason some companies publish open source code is to recruit contributors. Contributors already know what they're doing and are clearly passionate enough about the product to spend time on it for free, so they may be a natural hire when a position opens.

[exelius]

I think you're vastly overstating it.

The main reason most companies open source stuff is because they had to build something for some reason or another, the thing works, but they don't want to maintain it because it's plumbing and it's not mission-critical.

Sometimes it's easier to throw the thing on GitHub (where others might find it and at least use it) than throw it in your company's internal repository (where nobody will ever find it and it will rot away).

[eeZah7Ux]

Citation needed!

Most of the time it's much easier to leave stuff in internal repos than doing the effort to review and approve stuff for publishing.

[franciscop]

Well put, I see that as a combination of "better code through more eyeballs" and "great recruiting tool".