Wait a second. What kind of person would be ignorant enough to fall for this scam AND yet own Bitcoin to send?
If grandma reads this email, she won't know what a Bitcoin is. So she couldn't send money to the scammer even if she wanted to.
So who is this scam targeting?
Someone smart enough to follow the instructions (the target is supposed to buy bitcoin), but dumb enough to fall for it. In this case, they're not targeting grandma. Since the scammer has nothing invested, if it only works 0.000001% of the time, it's a huge success.
Speaking of which, I'd be morbidly curious to know the success rate of various scam types. I know that's impossible info to ever get, just sayin.