The point may simply be to move the attention away from the NSA, who are perhaps the real authors of WannaCry.
Makes complete sense.
To use the revenue generating argument from the OP article as a good indicator of the author is weak at best.
The other is an isolated nation that's decades behind on technology, only recently building weapons that can compete on a global scale, and struggles to feed its starving population.
It wouldn't be the first or even hundredth time that the US gov did something shady and pinned it on an enemy. It's less about the money and more about justifying their expanding powers.