That's one definition of "legacy". The other is "oh shit, this stuff isn't supported any more and is now a liability".
Which is a problem, because the longer you're unaware, the more the liability and unknown unknowns grow. Eventually, the liability and cost to replace are huge/bigger than it being an asset. The problem just gets harder; especially if you ignore it until it goes horribly wrong. See a comment above [0] for how this could happen.
Responsible, senior devs should be able to provide some guidance to the business at what point the system or sub-system is on that liability vs asset curve. "Not cool any more" isn't that kind of advice.