Probably because the small micro loans are worth so little now it is a waste of time. Who would put in the effort for $1 scams these days?
People have tried to (and sometimes been successful at) scam for as little as .001 before. I believe this was around the time that the price of bitcoin was around the price it is now, but had been going up instead of down.
I would say that since the price of bitcoin has been generally decreasing, there is less hype about it so people are going to be less likely to be willing to take risks with their bitcoin which means there are less potential targets that will fall for these scams