Ahh, after re-reading what I saw, this is actually the fact I saw:
They make creme eggs all year round, but only sell them for an exclusive period of time. The reason for this is they can't make enough to be able to satisfy an all year round demand.
So yeah, they have to spend a whole year making them to have enough to satisfy the demand there is for the exclusive time they do sell them.
So the reason they don't sell them all year round is because they simply can't make enough to satisfy the demand. That's pretty mind-blowing .