Aircraft are substantially more resistant to bad weather: you can fly an airplane into a hurricane.
Aircraft are also a lot faster -- it's unlikely that a thunderstorm will catch up with you (max speed of a storm is something like 50-80 mph) and trips are a lot shorter.
Airships are much closer to the storm speed and may need to stay aloft for several days. That makes it more likely that they'll hit unexpected weather and give them fewer options to avoid anything.
It's true that someone could do some shipping with airships and just eat the downtime due to weather. So far nobody has done that. And not for lack of trying: CargoLifter (mentioned elsewhere in this thread) went bankrupt on this idea.
Aircraft are also a lot faster -- it's unlikely that a thunderstorm will catch up with you (max speed of a storm is something like 50-80 mph) and trips are a lot shorter.
Airships are much closer to the storm speed and may need to stay aloft for several days. That makes it more likely that they'll hit unexpected weather and give them fewer options to avoid anything.
It's true that someone could do some shipping with airships and just eat the downtime due to weather. So far nobody has done that. And not for lack of trying: CargoLifter (mentioned elsewhere in this thread) went bankrupt on this idea.