"that's feature-complete and functional."

I get where you are coming from. That was my stance roughly 20 years ago too. I also note that you are quite clearly not daft!

You and I have different "jobs". I worry about thousands of systems on many sites, one of which is my home. I'm an IT consultant and am the managing director of my company. I think you are an engineer, perhaps retired ("12-year-old copy of a corpo CAD package and it works fine")

If Solidworks, Catia, AutoCAD or whatever (?) works then fine. You might like to firewall off whichever vendor's website/security systems might want to stop a 12 year old copy of a corpo CAD from working if it isn't licensed. It probably is because all of the above generally need a license service.

I worry about many 1000s of PCs and I think updates, patches etc are a good idea. If you are an engineer, then you will have to do your own "deploy, fix issues" cycle. IT is just the same.