You got an application that is free?

I got many. But some of them needed In-app purchases to continue the game.

Example is "The Walking dead season 1 and 2"
Only 1 chapter is free, It has 5 chapters. Only 1 can be playable by free.

Another 1 is "Lego Star wars trilogy"
Only 1 chapter is free again, and chapter 2-6 needed to pay just to play.

So whats your thoughts?
Why they would make a free app that is.... Only 1 part of the game is free?
Why they didnt made a demo/lite version?