Earlier quoted context omitted.
There are 2 possible questions. (1) - Why is a crutch like "anti-virus" software needed? Essentially trying to reactively cat-and-mouse hostile software that the OS has let execute on the computer. (2) Why doesn't Windows provide AV? Question (1) is more interesting - and (2) is addressed by other comments. I think both MS and their customers have very seldom prioritized security over even small compromises in functi…
The cat-and-mouse game is between OS security features and hackers. AV software is not a crutch, it's an extra level of defense. All OS kernels are vulnerable to malware - this is a 100% given at this moment in history. The question is how to mitigate this problem, and AV is one component of that, as are firewalls, network-level intrusion prevention systems, and a whole host of other security software. Maybe some day…
Secure operating system designs tend to simplify and take away stuff rather than add more bells and whistles.