To answer the rest of the question.
Recordings go "out of print" when the company that is printing the recording decides that sales do not justify printing any additional copies and the company's stockpile of prints have been exhausted.
Typically, vinyl and CD recordings, like books, are produced in a "print run" where a large number of copies of the same recording are produced at one time - typically thousands or even tens of thousands. The size of the print run is determined by how many copies the record company thinks will sell, but keeping in mind two factors.
There are overhead costs for each print run so that, the more copies printed, the lower the manufacturing cost of each copy will be
Unsold copies must be warehoused, which is also an overhead expense
For most recordings, there is a high initial demand and then a gradual fall-off. The recoding company's goal is to make as much money as possible by anticipating the sales curve and having enough, but not too many, copies to ship out to retailers.
If there is heavier than expected demand, or demand remains steady over time, then the company will order additional printings and the recording will continue to be "in print", possibly even indefinitely for recordings that become "classics". Otherwise, the stock of printed copies will eventually be exhausted, and at that point the recording will become out of print.
Some people reading this answer are thinking "does that really even matter with digital downloads"? And the answer is - sort of: some people like having physical media; but also, not entirely, as digital media is much less likely to go out of print, as printing and storage costs have been removed from the equation.