Hmmm, norther africa, middle east (Especially Israel and it's neighbours but also Shiite/Sunni neighbours), Pakistan-India, Russia vs Georgia, Korea, Russia-some minor former Sovjet State like Georgia, Balkans,...
Maybe because he doesn't want his civilians to suffer from duggin in in the cities. Maybe because it will not always be the US.
Or if weather restricts the ability of using air power. This for example happened during Desert Storm and Iraqi Freedom. There the good equipped ground forces (inlcuding tanks) made the difference and not air power.
Kosovo is another example. The west hesitated to enter with ground forces due to fear of casualties. There is no doubt that western forces could have punched the serbs into the ground but with how many casualties.
Nearly no one can hope of repulsing a US attack but one can make it as costly as possible. And that includes using all kinds of terrain not only cities.
You don't really want to compare Hannibals incursion with some ten thousand men into Italy with a modern mechanized combined arms campaign, don't you?
I am talking about a massive modern army invading a country. This army is going to maneuver freely without an enemy confronting them in the open.
As I said before.
You loose your airfields.
You loose your loose your supply lines.
You loose your communication.
And while this is happening the enemy is getting stronger every day you sit in your cities while you get weaker.