Why Applications are installed in different places?

I am talking here of mainstream applications such as MS Office,NAV,etc. Why are they installed in a way that different files go to different folders and not in one single folder? If applications are installed in a single folder,I believe windows will be more stable. Also easy to uninstall. I know that some applications rely on the dll to reside in the windows/system folder to speed up things but with the present crop of high speed processors I think this reason had become irrelevant.

 

I agree this is often annoying. The main reason seems to be that
system folders such as Program Files are on Windows search list,
and your new folder eg "MY-Office" is not. So the files that apps share with other apps in a supplier's product range are put in a system accessible Folder - that way, they are not duplicated.
Swings and roundabouts.
For example Norton Utilities and NAV use the same Live Update
procedure. It would be a waste of space to have Live Update twice on the PC.
What do you think ?
regards