What are the main drawbacks for anti-virus software?

AV software is difficult to keep up to the current revisions.

AV software can detect viruses but can take no action.

AV software is signature driven so new exploits are not detected.

It’s relatively easy for an attacker to change the anatomy of an attack to bypass AV systems

AV software isn’t available on all major operating systems platforms.

AV software is very machine (hardware) dependent.