Why did Apple Decide not to install Command Line Tools as default?
To answer your question, not many (relative term here) OS X users will install or have any need for command line tools because it is part of a larger group of tools to download. A large majority of regular, everyday OS X users won't be using these programs. However, you do not have to install Xcode to install command line tools anymore.
Sign in to Apple's Developer Downloads Page and then search for Command Line Tools.
Download and install the latest as a .dmg.

Related Question: How to download the Command Line Tools for Xcode without the Downloads for Developers webpage?
Alternative Way
As referenced from a Stack OverFlow post, here is an unofficial link to the March 2012 Command Line Tools for Xcode.