What were you thinking idle air?

Idle air, or the functional and cheaper equivalent, shore power has the fatal flaw of not being every where you might park your truck and need it. So, are you going to have a $10,000 APU and not use it when Idle Air/ShorePower is available? It's an either /or situation, and the market place has clearly chosen truck mounted APU, or more commonly idling the engines, which is legal everywhere including California if you have the clean decal on the hood. Total cost is the idea, and an APU is turning out not to be cost effective.
Best example: Walmart decided to mount an APU on every single tractor after Massachusetts sued them for idling their trucks several years ago. The could have easily and much more cheaply put shorepower connections on all the tractors and instructed the drivers to plug in behind any one of the thousands of Walmart stores. But even with that widespread availability, they decided against it.

 

@StudebakerHawk, thanks for your comments! The advantage of the APU is that it goes everywhere you go. IdleAir will never be at every place where you shut down for the night. However, we believe that both IdleAir and APU's can be part of a complete solution for drivers. IdleAir already have many, many customers who have APU's. Sometimes the APU's can't keep up with the summer heat, but often, drivers prefer to save the wear and tear on their APU's for when there's no IdleAir available. IdleAir offers ConvoyTV+Power, which is very popular among drivers with APU's. ConvoyTV+Power costs $1.49/hr +tax, which is roughly the cost of 0.25 gal/hr diesel for the APU, plus wear and tear.
Walmart is an interesting example, because many of their tractors do have APU's. However, as many drivers have noticed, Walmart doesn't always want trucks staying on their property. Also, there are more than just Walmart-owned trucks that service Walmart locations. So there may be other reasons - beyond straight dollars and cents for idling - why Walmart doesn't offer electricity to trucks.