Why are the cooking times on frozen pizzas always incredibly wrong?

Coking times are always approximate, as every oven can give different heat, depending on how good the seals are, whether it is a fan-forced oven, how accurate the thermostat and temperature gauges are, etc. It is always best, when cooking something for the first time, to keep checking it, to make sure it is not cooking too quickly or too slowly.

Just use the box directions as a guideline. You can smell when a pizza's close to being done, then start keeping an eye on it.

I've been cooking frozen pizzas since the 4th grade. It's not difficult.

Get yourself a pizza stone it will help on cooking it evenly. But inthekitchen is correct you need to play with the cooking times. Also you have to preheat the stone as well.

It usually says right on the packaging cooking times may vary according to your individual oven,

Ovens are different temperature. It always takes me WAY longer to cook them in mine. I do 25-50 degrees hotter and 10 minutes longer.