Because Walt wasn't trying to kill either of them?
Now Walt is a messiah, able to predict exactly how much collateral damage will occur from an accident. For all Walt knew when he took that drastic step he could have killed Hank and himself. It was a gamble. Same as when he poisoned Brock, there was no way to know whether he would have died or not due to the highly sensitive nature of the poison - and yet he still took that risk with a completely innocent child.
Walt doesn't give a fuck. Dunno why that's a revelation to you.