Supply crates power/tiberium/crystal ratio

I have noticed that the supply crates more often gives a power crate than it gives a tiberium or crystal crate. And I wonder why that is?

I thought it would be a good idea to maximize power production in my bases, as it can't be transferred between bases. However, maybe it wasn't so, because with the way it works, I get an abundance of power supply crates I don't really need, but always run out of tiberium and crystal supply crates. I think they should be more evenly distributed, that is all. It is a bit disappointing to kill a camp or an outpost for a crate, and only get yet another power crate.