Weekly points are there because WW assumes quite reasonably that most people don't eat the same number of calories every day. The WW program is meant to be a permanent change in how you eat. Real people eating in a realistic fashion will eat different amounts or types of food on different days. I can go out to a restaurant and eat a meal for less than 500 calories - I do this quite often at some restaurants. But, I don't always do that. Sometimes, I might eat a higher calorie food or I might have dessert. On another day, I just might be hungrier.
Weight Watchers realizes that so it sets a base amount that is the minimum that you should be eating each day. The weekly points are there as a guide to what the maximum is you should eat each week. WW assumes in its program that people are eating all of their weekly points. You don't have to eat them. I typically don't eat all of mine. But, I eat all of mine that I want to eat in a given week. If I'm hungry, then I feel free to eat weekly points. If I'm not hungry, then I don't have to eat them.
There may be some people that can go a lifetime eating the same calories every day and who never have a day where they want to eat more. My fear, though, is that most people can't realistically sustain that kind of the eating for a lifetime.