It doesn’t make a lot of sense to buy a small displacement engine in US.
It’s not about technical aspects or gas prices it’s about taxes. In US sales tax is a percentage from the vehicle price, the tax for a 50K vehicle with 3.6 or 2.0 will be the same, in many European countries they have import taxes for cars that are calculated based on the volume of the engine. For example, for 3.6 the tax is ~$12000 (yes 12K) 2.0 ~$2000, same vehicle with 3.6 will cost 10K more than the one with 2.0, this is why automakers are forced to squeeze more hp from less engine volume. There are of course many 2.0 on the market because they built a factory for those motors and so far, Wrangler is the only selling vehicle with it. What the benefit for the user? In EU ~10k tax savings, in US not so much.
3.6 isn’t perfect but is the best from what they have to offer.