Honestly I think the issue is not a matter of difficulty - its raw RNG. As I've been running 24 retainers for 4 weeks non-stop. Not a single light. The issue is that there is such a massive array of rewards (with more added) that it will likely only go down when the few that are up no longer sell and then you might see a trickle come into the market. The problem is that FF cannot really function under free market logic because the money never leaves the economy.