Yeah, nobody was fired for buying IBM…
I often argue from the security angle: closed source is security by obscurity. Well-chosen open source libraries are clearly better off.
I have the advantage that we develop custom software. Normally the problem we solve wasn‘t solved already or the licenses are very expensive. So the customer mostly doesn‘t care what tech we use.
I‘m more often challenged over the choice whether a standard software should be used or a custom solution is needed.