It is a very contentious subject, but some people argue that part of the reason the existing big manufactures don't put enough effort into making and offering ZEV is because they can't rely on the dealers to actually sell them. Reasons given for this is that the ZEV compete directly with the hybrid and gas vehicles on which the dealers have far greater inventory and profit margins, so they have little to no incentive to sell the ZEV.
If ZEV subsidiaries of the manufacturers could be guaranteed a chance to sell them then that might be cause for them to spend more effort on making them work.