There is basically no reason for them to contribute back. Using all available tools while restricting their own efforts for their own use creates a competitive edge.

The only time it makes sense to release something to the public is as a complement to one of their paid services.

Copyleft licenses were created for a reason. If you want companies to either contribute back or fuck off, use copyleft licenses.

This is, unfortunately, less and less true, when companies like Amazon will take some GPL'd software and make modifications internally and never distribute it. Copyleft licenses only apply if Amazon is going to distribute the software outside the company (such as by selling the software, or giving away binaries).

Then use a stronger copyleft license like the AGPLv3 that companies like Amazon are totally allergic to. Alternatively, use a license that offends the HR department of the corporation, like WTFPL.

Amazon does contribute to open source, though- https://aws.amazon.com/opensource/

It may be argued that they don't contribute enough, or that they aren't contributing to what you think they should be, but they certainly do contribute.

Pretty much every startup and company in our industry.

Red Hat?

I like clang