What would cause low toilet bowl level?

Some bowl levels are made that way, some leak out by a break or by syphoning because it is not vented correctly. Some evaporate because of non use, and some are simply not refilled because the refill tube is not in the overflow tube.

Your water level in the tank wants to be set at 1/2" under the top of the white overflow tube and, as Doug advised, check to see that the little tube from the top of the ballcock is securely fastened to the overflow tube. Good luck, Tom