Devs Use Closed Software

Depends on the software type.

Editor, diff tool -- something that can co-exist with open alternatives, and works similarly for all users? Sure.

A custom software with expensive support contract? That works too. Just don't be too greedy -- I have seen multiple "internal rewrite" projects because vendor was asking for too much money.

Something that needs lots of customization, but at the same time not that expensive, like a build system or a compiler? Probably not a good idea. I spent multiple days digging into source code of both our CI and our build system, and I was able to fix / work around the bugs I saw... But if they were closed source, it would be impossible. And the community is going to be much smaller, too.