There would still need to be money to make from doing so and a will to do it.

My company has a shitty old defunct group management portal that has been twice superseded and is finally getting shut down. But we have LLMs, why not maintain it in perpetuity? Because it's shit, nobody likes it, there are other options, it would still cost someone's time just to follow all the processes we have to do releases and keep things running, security testing, yada yada.

Adding more years of support to some shitty old thing is certainly going to cost them more than it makes them.