Network security experts: why are there so many layers of security, rather than a central method for securing all data end to end?

So I’m preparing for the CCNA exam and having fun learning about network security and all of these different security methods. A couple days ago though I heard about this encryption software called Veracrypt that is virtually uncrackable. The NSA hasn’t been able to even break it. It is basically used to encrypt hard disks.

But for networking, we apparently have so many different methods of securing network communications. SSL, WPA 2 AES, certificates to verify back and forth, and probably half a dozen other security methods for wireless networking.

Why not just have one central method using something like veracrypt to encrypt all communications from start to finish across wireless networks? Like, if you sent completely encrypted data with a safer distributed to the parties that are receiving the communications, much like a certificate, what would be the issue?