There is a finite amount of them - 2^32, some 4.3 billion - the limitation stems from using 32-bit values to express them. We cannot have more added, as the "capacity" of the 32-bit IP address value to provide different numbers has been exhausted by "assigning" these blocks of IP space - back in the old days of the Internet, large blocks of IP space were given to large organizations (such as Xerox mentioned in the article), now cloud hyperscalers are buying them back at a premium so their customers can use it to host things.