If I'm understanding Ctrl correctly:
Since 5A is fast and jump cancelable, it is necessary to VTC into 720 so you stay on the ground.
However, canceling VTC into 720 is (apparently) not allowed if it was a gatling VTC.
To bypass that restriction, you jump cancel 5A so it becomes a raw VTC.
In short, you are jump canceling 5A, canceling the jump startup with VTC, and then kara canceling the VTC with 720. my brain