Ballast resistor question

Part of the reason they MUST run so hot is, they are a ballast rather than just a common resistor. They are designed to average current through them due to changes in current and temperature. The change in operating temp of the resistive material, as well as it's alloy, is what gives the ballast it's regulating characteristics.

Common resistors can be calculated for operating conditions and wattage, and sized up in wattage to operate somewhat cooler