I know this pair

Father and son farmers, small acreage. They found an older but common model of tractor that worked fine on natural gas, cheaper. They buy them, convert them and lease them during harvest.

Why not more natural gas vehicles and less natural gas plastic containers?  Natural gas comes from oil production, more fossil is left in the ground if natural gas were more efficiently used in transportation. So, it may not be dense, but we already transport it. On net, it might be slightly more green when used in the mix of fluid fossils.

Like these folks:

As it turns out, there are very few technological barriers to overcome. In fact, converting existing vehicles to burn natural gas isn't particularly challenging. Unfortunately, if you tried to do it yourself, you'd more than likely run afoul of the Clean Air Act's rules against modifying fuel systems--a violation that could cost you up to $5000 in fines for every day you drive the converted vehicle. So if you want to green your wheels today, the only way to do it is by hiring a certified compressed-natural-gas (CNG) installer to do the job. To get the skinny on aftermarket CNG systems, I visited NatGasCar in Cleveland. It's a startup shop that augments gasoline cars by installing a parallel natural gas fuel system. They showed me their latest creation, a dual-fuel Dodge Caravan intended for airport taxi service. It starts on gasoline and switches over to natural gas once the engine warms up.

Aside from the regulation issue, why not?  Most homes have natural gas outlets, just fill up the tanks with a bit of pumping.  Less brown green than other brown green methods.