What are the reasons why a restaurant wouldn't offer a big Mothers day brunch menu on Mothers Day?

Being someone who has worked in restaurants for a long time, it is difficult to deal with two different menus at one time. There's planning the menu, buying the ingredients, prepping the ingredients, teaching the staff what you what done, getting the waitstaff up to speed, keying those items into the computer, and then dealing with the leftovers. Plus, you have to find space the store all these items before, during, and after. And if you don't have extra people, it might not be so cost effective. Given the economy these days, many restaurants really have to keep an eye on the bottom line.