You said a lot more than you probably intended. Microsoft created the Microsoft-loving, Linux-hating trade press in the 90's. Consultancies fell into line, and started pushing the theory to uncritical IT management that if you had a computer connected to the corporate network, it had to run a virus scanner. Period; full stop. Regardless of operating system.
I've never met anyone in corporate IT who actually does the math, and determines whether a particular threat vector is worth the cost of the preventative measure. The philosophy in the 3 Fortune 250's I've worked for has been: if it exists, it must be purchased/used/applied. In the 90's, yes, every WINDOWS computer connected to the corporate network needed the corporate AV running on it. Linux? Mac? Not so much. Even if they managed to get compromised, the chance that they would infect a neighboring computer were very small. These odds didn't justify the expense or the hassle of needing them to slaved into the corporate AV solution, no matter how much Microsoft diverted attention away from the very special problem that Windows has always posed from a security standpoint, how much they paid the trade press to paper over it, and how much they partnered with consultancies to push that line. They didn't care about the mainframe, did they? They didn't care about the Unix workstations, either. But Linux? It was the devil.
We have come full circle. Microsoft is trying their hardest to astroturf the message that WSL enables a lot of development workflows for which Windows has been a poor choice of late, and this requires them to "love Linux." So now Microsoft MUST release their Defender product for Linux, in order to be taken seriously BY THE VERY CULTURE THEY CREATED. As a guy who run Linux on the desktop for 19 years, and got my corporate IT (in the 90's) to consider Linux all the way to the point of them looking into a virus scanner for it (finding that Symantec didn't support it, and dropping the idea), the irony here is both delicious and sickening at the same time.
As I keep saying, I'll believe Microsoft "loves" Linux they day they create Office and an AD client for it.