Why not? Many people have old laptops gathering dust. They are too old to run modern operating systems, but the older systems are not up-to-date on security.Why? Why would anyone do this?
And Chrome OS is useful. As one example, because of Apple's inattention to the education space over the last 5-10 years, Chromebooks have become extremely widespread, and the preferred choice for many school districts. This would let parents put Chromebooks in the hands of their children without having to buy them. This is also great for the environment, as it repurposes an existing machine.