Efficency, especially when covered with solar panels. You could basically fly without fuel. Planes on the other hand are indeed much faster etc. but they only

Efficency, especially when covered with solar panels. You could basically fly without fuel. Planes on the other hand are indeed much faster etc. but they only are because they burn lots of kerosine. But all in all, as long as kerosine remains so cheap, airships cannot compete, except in niches.