Airships face three main problems, AIUI:
- They're slow (100km/h to airllanes' 600km/h), which means their flights are ~6x as long and thus their staffing costs are 6x as much.
- Airships still have trouble adjusting their buoyancy - if they pick up/drop off cargo, they become heavier/lighter and start to drop/lift up. That causes a bunch of problems.
- Weather screws them - as you can imagine, they catch a lot of wind with their sideward profile. And by definition they're lighter than air, which means they get knocked off course. Water ships don't have this problem because they're heavy as hell and literally made of steel, and of course because jet streams don't reach sea-level. The end result is that airships tend to fair-weather flights by necessity.
#2 can be mitigated and in the future might be solved, and #1 might become irrelevant if fuel costs get high and a niche for airships appears. #3 is a killer for reliability and safety both, though - you preemptively avoid storms by just delaying the flight until the weather prediction turns in your favour, which might take weeks. It just can't handle a schedule, because putting an airship into a storm is too risky. And if time isn't important then you can just put stuff on the cargo ship and then a train.