(tinfoil hat on)
They probably do, unfortunately many of us believe they and other companies might be writing some of these themselves to guarantee next years sales.
(removes tinfoil before coworkers notice)
My work has several hundred Linux servers. Due to policy/state law, we must have an AV on every server in our datacenters. You can guess how many hits we get on the Linux servers. It’s not only a waste of money, but of CPU cycles as well.