You cannot stay up to date permanently, because that introduces risks all the time. Once you earn money, there are layers to protect the money stream.
You can loose tons of money by not staying modern, that is true. But you can loose everything when you ignore a risk. The trick is to find a balance.
And all of that is not considering investors and their idea how the money should be used.
I suspect corporates don't really want to get stuck with so much legacy, they just don't know how to avoid it.