Because there are still bugs in this system. It is that simple. Not everything works on all PCs.
For Windows Live it's best to find a Windows Live support forum. My bet is some protection software is blocking a needed change but as I don't use any of the Microsoft Live software and only helped a few sort it out I can only share what it was. Specifically any of the protection software like Norton, Mcafee, Spybot teatimer among a few hundred others. I can't guess what you installed or if you EVER used a registry cleaner which trips up far too many softwares.
I have Windows XP Pro running on a 4 year old Dell XPS Gen 5 machine. Windows Live Essentials has shown up on my Windows Update page and I have tried in vain to install this package.
I have gone to the trouble page after the installation fails and complied with everything that they say could be wrong. AFAIK.
I have used End It All to close everything except the internet connections.
The Windows Live Essentials does actually install. It begins by notifying me that there are no conflicting programs found. Then it installs the entire bundle of programs. Then when the overall status bar reaches 100%, the thing automatically Rolls Back everything until the status bar goes back down to 0% and the installation fails. This is really throwing me. How can the installation get to 100% and still fail?