Angioplasty is the technique of mechanically widening narrowed/obstructed arteries, and it's usually done to treat atherosclerosis. So basically this is the process of putting in almost like a balloon in your arteries to widen it for proper blood flow, this is why it is called a balloon catheter. Heres a picture below to show how it would work. So the reason why Angioplasty would not be a wise decision to treat an aneurysm is that an aneurysm is basically a blood-filled bulge in the wall of a blood vessel. So if you would use Angioplasty as a treatment it would not work ,and in result the actual aneurysm could/will burst from the pressure of the balloon catheter placed from the Angioplasty treatment which can lead to death.