The Torah says any ill-gotten financial gain on Shabbat will be lost through theft, illness, etc. The "chacham" store owner ultimately only fools him/herself. The purpose of kashrut - as with all mitzvot - is to create a G-d-fearing person (“all is in heaven except the fear of heaven”) and a holy nation. Any restaurant owner who would keep his/her store open on Shabbat is a person who would have followed the golden calf at Mt. Sinai, as they are clearly more concerned with making money than even the 4th of the Ten Commandments. (Remember and guard the Sabbath…)