Why doesn't Norton block Malware?

I relative of mine recently was infected with TROVI malware.  He runs the Norton Anti-Virus that comes free with a subscription to COMCAST.

Why doesn't Norton Anti-Virus block all the things that Malwarebytes Anti-Malware remover supposedly find and remove?  Note that for TROVI, Malwarebytes couldn't get rid of it either ... I had to rebuild the system from scratch to fully remove it.

Seems like there are a lot of things out there that I would call viruses (you might call them Malware) that Norton should be blocking.