Leica second hand values have settled back to realistic levels after the scarcity/demand induced by the M9. Back in ~2010 it was very difficult to find a camera and Leica lenses to go with it. Used prices were often higher than retail.
The M240 was an evolutionary release and not revolutionary like the M9. Therefore, it didn't necessarily generate the same degree of demand, nor inspire some M9 owners to upgrade. At least not immediately. Yet the technological improvements in the M240 likely broadened its appeal to those looking for a compact full frame camera but not necessarily interested in RF. Leica's production expansion allowed them to produce more products more quickly. It's possible they may have slightly flooded the market with M240 availability. For a time it was quite easy to find demo bodies at considerable savings. I haven't looked recently, so not sure if it's still the case. I'd guess Leica probably has sold as many, if not more M240s than M9s. That's a lot of FF digital RF cameras a step away from being on the market. The more there are in use, the more will eventually become available secondhand. And the M240 is coming to the end of its product cycle. In fact now overdue if indeed Leica had been on a ~3 year cycle like with the M8 and M9.
I prefer the way the market is going now. Those who want and can afford to buy new have that option at full retail. Those looking for new at better prices can import from the EU and still save a fair amount over US retail pricing, despite the current 12% 'exchange rate' adjustment/sale. Then there's the availability of demo product (bought a body and a lens this way) with warranty. And finally, somewhat depressed secondhand pricing relative to the bubble of the early-mid M9 lifecycle has dropped the cost of entry for those wanting to get into Leica without the budget to buy new...
And yes, the strong USD results in secondhand values that are relative to the global market and not necessarily relative to the somewhat inflated US retail pricing set by Leica.