Here is a serious question. What if you did work in a Windows IT shop and when the security auditors come around you say you rely on Micriosoft Security Essentials? Is that ok or is there some reason IT professionals think the security software has to be from someone other than the OS maker? Why don't other industries have the same opinion? Nobody asks what brand of airbag I use in my car, or insists that my deadbolt be made by a different company than my regular lock.
Your short answer is M$ lacked a nice server management system when they first rolled this out. Vendors like Symantec and Macaffee...they put a lot of effort into this server front end long ago. As once a company is hooked...its hard to pull it out sometimes. If any better in the couple of years since release I do not know in regards to ease of admin and such for many computers.
I liked M$' stuff when I ran a pc (mac conversion was 4 years ago). Home use fine. It didn't have a nice admin server front end though. I am an admin in mixed shop that favored symantec long ago. I have 1300+ clients on my network.
One of its good things from an admin aspect is its Symantec Endpoint Protection Manager server setup gives me lots of convenience. Package pushes, reporting, policy control, remote virus investigation and scanning (if I get hits on reporting I am pretty sure are false positives I can with a few clicks get detailed reporting and run scans on the suspect with the user never even having to be bothered)...over the years they have gotten this pretty good.
In terms of audit the reporting is also nice. My last audit I sat down with my auditor and went down the list of items. Screens shots of server config, policies going to clients and actual client reporting. Was not very painful (well less painful than other areas I also am lead on lol). Only leg work on their part was spot checks on various sites. Random sample client check bounced off server, good to go.
Now if M$ got better here I don't know as I said. They should have released a rudimentary server at launch of the the "home" client imo. This had companies go well lets go to the other guy if starting out. Those other guys...to keep up license renewals get real friendly. Symantec sales team is pretty good. Get to seem them once if not twice a year. They work hard to keep our renewal money flowing. And offer up other services, ofc.
That and in our case like I said I have mac's in the enterprise. Symantec supports that. Macaffee I believe does as well as do other known names. In one console I see what is going on with my windows and my macs. Something I can almost guarantee M$ would never support. I remember a great vm software app for windows called virtual PC. Did windows guests nice. Did linux guests nice too. Then M$ bought the technology. And for mysterious reasons (not...) linux support went away (unless you worked out some complicated work arounds).