Beef loin cuts are non-Kosher because of the presence of the Sciatic nerve array. The tradition goes back to Jacob. There are specialists who can and do remove sciatic nerves but your Porterhouse/NY Strip would be reduced to stew meat cubes. Here's the Kosher beef chart:
Consolation here is that brisket is A-OK, so are Ribeye steaks, big ribs, and standing rib roasts. Fair is fair, we smile at the laws that say a fish without scales is treif and that a bat is a bird, but them's the rules. Of course I cannot/do-not entirely keep Shabbat (I'm posting to you right now, obviously) but Kashrut dietary law is something I adhere to.