Microsoft do exactly the same, and have done for over a decade now:
> Malicious Software Removal Tool is a freely distributed virus removal tool developed by Microsoft for the Microsoft Windows operating system. First released on January 13, 2005, it is an on-demand anti-virus tool ("on-demand" means it lacks real-time protection) that scans the computer for specific widespread malware and tries to eliminate the infection. [...] The program is usually updated on the second Tuesday of every month (commonly called "Patch Tuesday") and distributed via Windows Update, at which point it runs once automatically in the background and reports if malicious software is found.
> Having something as simple as a functional-equivalent to Windows Defender with its own icon in Control Panel
MSRT is independent from Windows Defender.