Most PCB manufacturers have a min order of 5.
They’ll be glad to send you just one for the same net price as they sell 5. If you just want to take one, they’ll throw the other 4 away.
They tend to make them in panels of multiples to keep unit costs low. It takes just as much labor to make 5 as to make 1, because labor is the largest cost.
Often they will make more than 5 in a panel, and save the others as spares in case they don’t pass QC. They prefer to work in step and repeat as many as they can on a standard-size blank.
Read More: Prototype PCB Assembly