Temporarily, the economy.
But longer-term, the bigger issues are marketing and perception -- among potential ebikers, and among bike shops.
I've been soldering electrical bits for 40 years, so I think I can say this: The future of ebikes doesn't belong to folks who can solder. It belongs to the broader market of people who buy their wheels for transportation, for fun, or for image. Long may ES prosper and may the hobby community push the bounds of the possible, but that's not where bulk sales will come from.
In Holland more than a quarter of bikes sold are ebikes now. Infrastructure is certainly a big reason, but so is the realization on the part of the bicycle selling community that they can move ebikes and make more cash from them than regular bikes. (Besides costing more, ebikes generate more demand for tires, chains, replacement batteries, etc.) Over half the revenue coming in to bicycle shops in Holland comes from ebikes. Once North American retailers figure this out, they'll start pushing ebikes as they previously pushed disc brakes for the masses and carbon-fiber everything.
Mass-market bicycle manufacturers are clearly ready to jump in. Have you tried an electric Trek lately? They're expensive and equipped with Bionx systems... and they work beautifully. Please don't tell me you can build something more powerful for less -- of course you can. But it is an example of a smoothly-integrated pre-packaged system that just works, and has a Brand Name behind it. They'll sell, especially as the economy recovers.
I love tweaking systems (I've reconfigured my own Bionx system to better suit me and my recumbent bike, and added a DC-DC converter to support my lights) but I know I'm not the mass-market customer. I'm also a bike commuter (15 miles each way) and that doesn't make me the mass-market customer either. Increasing numbers of ebike purchasers are commuting and displacing their cars, but most still have other reasons. Maybe they're not strong cyclists, or cyclists at all. Maybe they're aging and their baby boomer knees need some help. Or maybe they're thinking green or just think it's cool.
The forthcoming issue of Momentum magazine will talk a bit about broader ebike culture. (I know - I wrote the article.)
Or you could have a look at my own site, where I hope to reach beyond the hobby community to address the needs of the broader electric cycling community.
Charlie
http://ElectricCyclist.com