Where are you getting this information from? EB-1/2/3 are clearly visas issued to people [0]. It is true that many people may adjust status to EB-1/2/3 while already in the US in another status, but they are certainly visas still available to people. As I understand, due to the quota system it can be very difficult for folks born in certain countries to receive them (due to quotas) and they end up waiting for many years.

[0] https://en.wikipedia.org/wiki/EB-1_visa

EB-1/2/3 are employment based green card categories. And being employment based means that the applicants need to be employed in the US before being able to even apply. In most cases, the applicants are holding the H1-B visa while their EB-1/2/3 green card applications are ongoing.