Because it has long been known that networked apps are a huge security vulnerability. Your system security is only as good as the security of the least secure

Because it has long been known that networked apps are a huge security vulnerability. Your system security is only as good as the security of the least secure networked app running on it. So as OS and network security improves, attacks via networked apps are becoming common. Securing ALL the networked apps would be a huge cost to industry, so they are furiously trying to ignore the problem and have been for decades.