Crosswinds. Remember, you're in a giant balloon that doesn't have independent propulsion as it has negotiating rights with the sky. If you're headed north and the only north wind is at 3000 ASL and the ground is 2700 ASL, then you options are horsing at three hundred feet off the ground or engaging in Dynamic Lift Exercises higher up and hoping you don't hit a southbound wind.Mind you, I'm having difficulty working out why an airship might want to hug the ground at any time other than take off and landing.
Everything has problems in modern cities. Most major metropolitan centers in the US have a altitude "floor" of five to eight thousand feet, below which you are technically endangering the city by flying at reckless altitude.Good god airships would have problems in modern cities