Are antivirus necessary in Linux?

When I was 100% in Windows I used Kaspersky, but since my subscription expired I'm trying to go somewhere else like Bitdefender, but the problem is that now that I have more Linux machines and my future ones will run on it most of the time (for programming and stuff) do I really need an antivirus on Linux? (Since they say more and more viruses are made for Linux for servers). Also, if said fact was true, then why aren't mainstream antivirus available on Linux? And finally, what would be the best antivirus that is mutliplatform? (Windows, mac and mostly Linux).