if there was a high demand for used 500e's, they would shoot up in price on the used market, and they would no longer be affordable. They are are fairly rare cars which are low in price due to extremely low demand.

You could almost say the same for the i3.
I'm not suggesting that the current used EV market is a permanent situation, though. Ten years from now, there will be a much larger supply of quality used EVs available,
The major problems are:
1) Electric cars are more expensive to build due to battery pack cost. (Chrysler claims they lose $10K on every Fiat 500e they sell).
2) Manufacturers throw a few electric & hybrid cars into their lineup for one major reason - to help them meet the fleet CAFE, EU fuel economy, and California zero emission requirements.
3) Dealers really don't want to sell electric cars - 50% of Dealer profit is from after-sales service, and electric cars on average require only 1/3rd the service of an ICE vehicle.
Electric cars sell and are in demand in a few small countries because of normal driving distances well within current battery range, extremely high gasoline prices, and a good public charging infrastructure. Denmark comes to mind as one.
In the USA, none of that exists to really drive heavy consumer interest and sales.
Mark H.
2015 i3 Rex, Capparis White, Tera World, Technology & Driving Assistant, Parking Assistant, Harman Kardon Audio System, 19 inch 427 wheels, EVoInnovate EVSE