There's a lot going on with US gasoline consumption:

1) land use decisions are pushing people further from workplaces

2) consumers are switching from the "car" class of vehicle to "light truck" which is negating fuel efficiency improvements [1]. There's a lot going on here, from people getting larger vehicles for perceived safety, to better comfort, to just having more money to spend on larger vehicles. Plus, all those people who think they need a truck despite using the bed once or twice per year.

3) Demand for gasoline is incredibly inelastic in response to price, with huge price spikes having almost no change in gallons of gasoline even as consumption in dollars spike [2]

[1] https://thenextweb.com/shift/2021/01/12/despite-ev-growth-ga...

[2] https://www.eia.gov/todayinenergy/detail.php?id=40893

MPG is a measure of efficiency, so it makes sense that it increases. To support your argument, you would need to demonstrate a corresponding increase in vehicle miles traveled per car, so that total gallons of fuel burned (i.e. energy) is constant or increasing.