Grocery stores don't sell as many steaks in a day as a busy steak restaurant does. They also sell all of the other parts of a cow and have competing food items for sale as well. Plus they pay their staff higher wages because they aren't tipped and have other overhead costs that impact all of the things they sell.

Restaurants are all about quickly moving a comparatively smaller number of items as quickly as possible. That means they buy specific types of things in bulk and have lower costs to get them to the customer.