Why do so many parents let thier kids misbehave in resturants?

Why is it that soooo many parents will just chose to ignore the annoying behavior that their child/children are displaying? I understand that when a toddler throws a fit, the best way to combat it is to ignore it. But why must they ignore it IN the resturant? When my daughter reaches that age I will remove her from the building and let her throw a fit either outside or in the car. If that means that I spend the rest of my meal in the car with her just so other paying customers can eat peacefully then I will. At certain places it is more expected then other. When I go to pizza hut or ruby tuesdays I expect that there will be many families and most will have at least 1 maybe more obnoxiuos kid with them. But there are other places that we eat at where I just can NOT accept this behavior. We have many great 4 and 5 start resturants where I live and they are generally very pricy. Last time we ate at one there was a couple whos child was playin under OTHER peoples tables!!