The old unmaintained ISDN hardware for which the code has been removed is likely 20 years old, or so. The perfectly good laptops are usually 3-4 times younger.
FreeBSD and NetBSD aren't going anywhere and can be used for older hardware, for the amount of production and load bearing use Linux sees there's an enormous amount of cruft and garbage in it.
That's good for your personal computing, but a renewing forest fire is good for all sorts of organizations. And species. It's a very good algorithm to run.
It's naturally de-ossifying and forces uptake of new methods and practices.
It gives you an opportunity to question assumptions and do things greenfield again.