Calling in an airstrike usually takes time. Even if you have Close Air Support (CAS) available munitions might not match the target. Anti-personnel weapons won't work against tanks and precision anti-tank rounds aren't of great use against people. There are things like DPICM (Dual Purpose Improved Conventional Munitions) which can be effective against both, but a loitering aircraft might not be carrying that. Getting an aircraft to you with the right ammunition might take awhile. And there may be no aircraft available at all. I ran into this in Iraq. Our convoy ran into a friendly tank that had outrun its Infantry support. We dismounted and waited for over an hour, taking hostile fire constantly, until a Kiowa Warrior (armed helicopter) could make it to us.
Artillery, fast movers, helicopters, mortars from the Infantry and even naval gunfire and more are all capable of providing "fire support". There are small groups of experts who manage all these assets. Such a group is called an "FSE" (Fire Support Element). These folks look at the situation, analyze what available asset is best suited for the job and assign them appropriately. It a complex job. That's why the military works in teams. Requirements vary. Available assets vary. It takes the whole team to get the job done.