Sometimes they accidentally weaken the algorithm (like by chopping it's key bits in half through a weak RNG). Crypto is hard, even when the scammer probably has a good grasp. Which is useful in this case.
It's hard to (a) rapidly, (b) silently, and (c) strongly encrypt a critical portion of a business's network.
You can probably choose two.
Sometimes they accidentally weaken the algorithm (like by chopping it's key bits in half through a weak RNG). Crypto is hard, even when the scammer probably has a good grasp. Which is useful in this case.