I think this is a disadvantage many developers face. Their entire life's work is tied to some proprietary product and when they leave their company (or get laid off), they effectively have nothing to show for it. Sure, you have the experience and the knowledge gained, but nothing material. This is why I encourage devs to turn proprietary work into something that's "theirs." For example, writing blog posts about your work, contributing to open source (or convincing your company to opensource something you worked on), side projects, etc.

It's unfortunate that we have to do this extra work, compared to, for instance, researchers in academia or, say, a Linux maintainer, who "own" their work (or at least get credit for it).