I've worked in a bunch of industries and places over the years, and this is not just a tech thing. Like, there's a reason that saving a day in the library with a week in the lab is a pretty famous saying.
This was a CTO burning funds, and that does not even cover the maintenance costs, especially as the original library changes and becomes drastically more modern.
You argumentation assumes that the goal was saving money.
On the other hand, if the company's goal is to become a little bit more independent of this library (and their licensing fees), this approach often makes a lot of sense.
On the other hand, if the CTO's goal is to grow his empire with no regard to the well-being of the company, this approach makes a lot of sense.