Because it acts as close to direct dealing in an online platform. Not having to deposit any money on the site is exactly how people want things. One doesn't go to Amazon and transfer money first to the Amazon site and then to the seller. In essence it is the closest you can get to a CC transaction as you can get with a market. They have eliminated the 'middleman' while providing a very nice platform to work from.
Since everyone knows that those who deal in crime are typically on the cutting edge I would not be surprised if Hansa is actually able to go mainstream. It's the simplicity of it that makes it worth so much.
In fact I see the value in it so much that I would donate just to keep it active. Wouldn't be much, but I would donate.
My favorite market, don't understand why AB doesn't do this.