Why doesn't the paint stick to new ingrain wallpaper?
I would guess that your issue is that you didn't prime first. 

From Wikipedia:


  A primer or undercoat is a preparatory coating put on materials before painting. Priming ensures better adhesion of paint to the surface, increases paint durability, and provides additional protection for the material being painted


You buy primer from the same store you would buy paint.  Primer goes on first, dries, and then you paint your final color on top.