Wouldn't it be nice if security threats remained the same? We would only have to implement a single type of protection for each risk -- and that's that. No need for a deadbolt because the regular doorknob lock works. Car alarms were never invented because door locks worked fine. Cybercriminals couldn't shut down your network or ransom your files because you had anti-virus software installed.
Unfortunately, that is fantasyland. However, sometimes we treat our networks and endpoints as if they operate in that idealized world.