Probably the installed base of gasoline-powered internal combustion engines has something to do with it. A lot easier (goes the thinking) to change gas into gasoline than to retrofit every vehicle out there to work on natural gas.
I’m all for the use of natural gas. The use of LP gas is used within the U.S. exisiting gasoline powered vehicles are easily converted to use LPG. BTW I heat my home with it. Seems it’s more efficient than fuel oil and a Hell of a lot cheaper.