After all, people believe they need antivirus software to stay safe (the fact antivirus software can be worse than the virus doesn’t change people beliefs) so why not buy the one that’s already installed on their PC?

Or another way of looking at it, Google pays Apple billions each year to make Google the default search engine on iOS, because Google recognises the power of defaults i.e. people are lazy and will use/buy whatever’s in front of them to avoid doing any work looking for alternatives.