Tl;Dr: I believe it takes advantage of tech-illiteracy.

My experience has been that McAfee pays for PC hardware manufacturers to include their service as an install with their drivers. This results in people seeing "Oh my new PC has McAfee antivirus," and it becomes their main antivirus by merit of always being in-your-face, then it eventually throws popups that say "Your antivirus is expiring, pay us!" To which if that's become your go-to, you'd likely pay without thinking much of it. Most people just aren't tech literate enough to take action on things. It always blows me away just how bad the common human's tech literacy is, like even 2FA services aren't understood by most people, heck most people dont even know how to uninstall a program on Windows.