It gets even worse with product activation.
Even if something is proprietary but without activation, you can sort of preserve it. I can spin up an old version of WordStar in MS-DOS on my computer, and open up old WordStar documents. I can start up Windows 3.1 if I want in a VM. It's not as good as something open like LaTeX, but it's not completely useless.
If you use Adobe CS, and Adobe goes under, changes business models, or takes down its activation servers for any reasons, your life's work might be dead. Few corporations survive forever. Even fewer products do. That's why a lot of us avoid rights-managed or some types of cloud-based software for critical work (although a lot of cloud-based has very good export options, so I don't hesitate to use e.g. Google Docs).