Why do I always get sick at restaurants?

We can't really answer because we don't know what you mean by "get sick." Do you mean you actually catch some sort of disease or virus? Do you mean you feel "sick at your stomach" or get diarrhea? What symptoms do you have and which specific restaurants have you tried?

This sounds like a generalization because it's very unlikely that you "always" do anything - statistically speaking, it's almost impossible to get identical results every single time. You probably feel sick after going to certain restaurants, or during certain times of the year (for example, cold and flu season, when almost everyone has some kind of virus).