I never thought of it before this ,but microsoft bundles and integrates so much useless crap into there products .Why have they not bundled security advice and an anti virus ? you would think doing that would save them money and headaches, how many customers do you think call them every day cause "my computer don't work and i don't know why but ..........."
If you think these words you said logically you will see that this never will happen. They cannot bundle an AV software due to the fact that they will have to maintain it. So let's say that they had bundled AV on Windows 95, a decade ago. A decade ago there was no such hassle about virus. Worms had not appeared yet. So imagine all these W95 yet clients what would do with a useless AV product embedded on their OS? Nothing. Things with worms changing on a daily basis and Microsoft would never cope with these kinds of updates. Moreover AV products tend to not like Windows OS'es....at least in critical servers or cluster servers still is a headache to implement an AV solution.
In conclusion I could write a book about why MS would not embedd an AV solution to its products but I will leave this to your imagination.