Antivirus and anti-malware is part of computer science/software development that is ever changing, and each and every product needs to be constantly updated.
Behind each product, there is a team of developers, technicians, virus and malware researchers, and anti spam technicians, and coders that work all hours, shifts spread throughout every 24 hour period. That is just the back end. Then you have the people working on the user interface to make it as easy to use as possible, and fast! The product testers, who ensure it is bug free so your system does not crash, and that it "communicates" with every known program that could possibly be installed on your pc.
The team that keeps on top of every new piece of malware whether it spreads on malicious websites, on links through emails, on Twitter though direct messages or tweets, or on Facebook through funny pictures of puppies and kitten that people spread, heck through charity causes saying "if you Like me I might hit my target of cancer treatment in America" etc etc.
People who keep up to date on every single development in the world of email and web threats. People who make it their job to know every new worm, every new trojan, every new security threat, networks with black hatters and white hatters alike.
The team that markets the product, updates the websites with every new feature, so that you know what to get and that you can stay protected.
This is the surgical team that protects your PC, that knows your pc like a doctor knows your body, and knows all the internet threats like a doctor or specialist in new and emerging health treats.
And you expect it to be FREE? 
And you know what, most of the best solutions for home users are actually Free.
But, you should not take it for granted, there is a whole team of people working their socks of worldwide to ensure your pc is protected, whether you chose to educate yourself or not. 