The D&D Starter Set for 5E says that it is for 4 to 6 players.
https://dnd.wizards.com/products/tabletop-games/rpg-products/rpg_starterset

The D&D Essentials Kit says it is for 2-6 players. (Look at the top of the Boxes picture.)
https://www.target.com/p/dungeons-dragons-essentials-kit-game/-/A-76151594

So if they wanted to just do 4 players. It is part of the rules. I hope they give us 6 though. smile