Then the agencies are endangering their own countries. It is simple math - the world produces much more geniuses that NSA employs (or GRU or anyone). If you deliberately introduce weakness someone will find it. And the entity may not be friendly.

The problem comes because the win of the cold war somewhat skewed the western view of their own capabilities.

When NSA had adversaries that they deemed worthy - they took the effort to strengthen everyone's communications. Right now while looking at the others with disdain and (wrongly) refocused the efforts on terrorism - they prefer weak networks.

Of course there will always be entities who try to break the system - either through technical, political, or social means. Fortunately the existing agencies who had enough power to do this have lost their credibility, so I doubt they will be steering people back anytime soon.

I am not sure if what I said above is even possible, but I hope it is. Trying to remove the side effects of humanity from something created by humans is not an easy task.