A handful of likes on a Facebook post barely registers, to a viewer or to the platform's own reach mechanics. Setting the floor at 20 instead of 1 means every claim actually moves a post somewhere, rather than technically working but not accomplishing much in practice. Fifty sits at the other end, enough to make a real difference without needing to look inflated.
You choose the exact number within that 20 to 50 range yourself through the quantity field. Nothing gets assigned automatically here.