Why? Well for one thing, she scares the life and soul out of her students. I don't mean awesome by what I usually mean it. Usually I'd say MOE or WIN or EPIC WIN or DIES FROM MOE OVERLOAD and stuff. But Izumi is different. Her's is a whole new kind of awesome. The deathly-make-you-wish-you-were-dead awesome however.
Now we all know where Ed learned his fist of the floor trick. Goddamn students imitate their masters down to the hair's grain.
Yes. Izumi is so wicked, its better to have created a homunculus than to have her as your teacher.
Though, if I were Ed and Al, I think I'd already have gotten used to it by now.