Why is the present simple tense used for an event that is in the future?

I would like to know the difference between "be going to," the present continuous, and the present simple. We use one of them when we talk about future, but I can't differentiate them. For example:

The holidays start next week.

Why can't we use:

• The holidays are going to start next week.


• The holidays are starting next week.


• The holidays will start next week.