Because of the planetary alignment of of the solar system to the horsehead nebula in the orion constellation.
Seriously, if by prayers you mean ones given to gods, there is nothing supernatural nor divine about it. The same would happen no matter to who or to what your pray to. Everything happens for a reason, and if your prayer was answered it is because of a series of events that led to it, not because of divine intervention. Things that happen are the consequences of your actions. For example, you would pray that you win the lottery, but you never buy a ticket, would you still win?
Also, faith, no matter to which god or even to yourself, is a big factor. Positive thinking helps create a favorable situation towards getting what you prayed for. It gives you the confidence to act, thus getting results.