Why are airships limited in the height they can attain?

Airships are limited in the height they can attain primarily due to the decreasing air density at higher altitudes, which reduces lift generated by the buoyant gas inside the envelope. Additionally, the structural integrity of the airship can be compromised at higher pressures and temperatures, as well as the need for sufficient atmospheric oxygen for combustion engines in hybrid models. Finally, operational factors such as weather conditions and navigational challenges also restrict their altitude capabilities.