Blax_Hydralisk
Restricted
Depends ont he attack. Not all attacks use the same amount of chakra, and not all people have the same amount of chakra. Kakashi's biggest chakra drain is the MS. Besides, Kakashi and Naruto don't do their big chakra draining attacks when they're already low on chakra. They do it and it drains them so much that they become low on chakra.
Itachi was already at the end of his rope. He was literally falling apart. When you're already low on chakra, that's not the time to use your big chakra draining techniques. He literally ran out of chakra, whereas Naruto and Kakashi just get so low that it causes them to passout. Not too mention that it was a large burst of chakra being drained from him, so that would explain why he didn't have lose conciousness first. He went from like 10%, to to -5%, in under ten seconds.
Why did he he do it? Because he has no choice. Itachi had two choices. He could either take the undodgable lightning strike to the face and die instantly, or he use this summon and possibly survive. He was just out of options.