windows 7 don't include .net 3.5 why?

i set up windows 7 two days ago. But i downloaded .net framework 3.5 . i think windows 7 included .net 3.5

From stackoverflow

• The question is not very clear! But Windows 7 comes with .NET 3.5 pre-installed. I installed an application on it a couple of days ago that requires .NET 3.5 and didn't need to install anything first.