Not the person you're replying to, but in any reasonable organization with automated software deployment it should be easy to pool machines into groups, so you can make sure that each department has at least one machine that uses a different anti-virus software.
Bonus, in case you do catch a malware, chances are higher that one of the three products you use will flag it.
So you have multiple AV products and you target those groups. You have those groups isolated on their own networks, right? With all the overhead that comes with strict firewall rules and transmission policies between various services on each one. With redundant services on each network... you've doubled or tripled your network device costs solely to isolate for anti virus software. So if only one thing finds the zero day network based virus, it won't propagate to the other networks that haven't been patched against this zero day thing.
How far down the rabbit hole do we want to go? If you assume many companies are doing this kind of thing, or even a double digit percentage of companies, I have bad news for you.
Bonus, in case you do catch a malware, chances are higher that one of the three products you use will flag it.