If you notice on the physical booster packs, it even has a disclaimer on the back that says that although the chances of getting a foil/epic are 1 in 5, this ratio is not guaranteed to be present in...

If you think about it, the odds of NOT getting a foil are 80%. 0.8^13 is a little under 0.055, so there is approximately a 5.5% chance of getting no foils in 13 packs.

It kind of sucks, because...