The median person does not have $10k sitting in a checking account that they can easily withdraw. My gut feeling is that the threat of kidnapping is a lot more serious in some countries. The US maybe not so much.
That's true, finding someone with 10k is not as easy as picking a person at random, but it is as easy as driving to the right parking lot and picking a person at random.
With crypto, no bank or other middleman involved, it's like stealing physical cash/gold/diamonds from someone, if you know they have it in their possession, so violence can be a lot more successful at coercing a change of possession.