Don't most companies seek a supported product, like yWorks or Tom Sawyer Software in the case of graph layout?

Isn't the EPL "weak copyleft", so LGPL-ish? Would companies raise similar issues about glibc and GNU libstdc++? Just curious.

True, and in fact I am aware that other teams look for paid solutions where graphs power the core features of their products. For us, it is a small feature, so we were looking for the "least trouble" path.

I don't know enough about all those other libraries and their licenses, but I do know that as long as we don't ship those libraries, especially modified versions, it's likely ok (of course that's simplified). Some internal tooling depends on GNU tools but we are just users. For things like glibc, it's just a standard system library, so linking with it is not a problem. (I am sure legal has looked at this.)

But GPL/LGPL software is definitely the minority of software we use in any way. Basically they need to be avoided as much as possible.