Cargo Airships Are Happening

The (biggest) problem that keeps airships from practical use is that they are huge sails. Big sails mean even small amounts of wind can be powerful forces acting on the airship. In the air a big push from the wind might be safely managed, but if you're near anything solid such as the ground, you can get smashed to bits.

To safely operate a suitably efficient (large) airship, we'd need both huge specialized docks with extremely strong mooring structures to keep wind from smashing the airship into whatever is near it, and a system (such as a 3-axis propulsion system on the airship) that is capable of counteracting wind force acting on the airship when it's near the ground or other solid objects and not docked.

Despite the many attractive advantages of airships, there's yet been anything like a good solution to this problem. There are other challenges too (what do you do when you drop off your cargo and the airship wants to shoot up into the air? Vent gas? Rapidly compress your gas?), this is just the biggest.

What makes you think "docks with extremely strong mooring structures" is a particularly difficult problem to solve? A giant metal hook anchored in concrete attached to the ship with some steel cables doesn't seem like it would be that difficult for a team of smart engineers with a multi-million dollar budget to figure out a good design for. Certainly not so difficult or expensive as to threaten to make the entire concept nonviable.

Historically the difficulty isn't in building the mast, it is in preventing the airship from being smashed into the mast by the wind. Or in dramatic cases flipping end over end because it was only moored on one location.