While you could argue VM are more secure, other security tools like BSD Jails or containers could offer a similar level of security for a fraction of the resources that QubesOS uses.
And if I am really being honest, not many people need that level of security as the main goal of Qubes is to prevent a system compromise, but most people have cell phones, cloud accounts, and are getting their uses names and passwords leaked through security breaches all the time, something that Qubes cannot prevent.