> diesel cars that weigh less than a Honda Accord.

It is taxed less than gas in lots of Europe where that is more common. You also need to factor in mpg vs gas, where it is higher, so more road-wear pCO2 was part of the debate in Europe, even though it is longer carbon chain so worse co2 ratio per calorie, the engines are more efficient. Diesel is worse for local air, better for long term co2.

There are a mixture of factors and lobbying behind the differencs, road wear is one. Farm fuel with no road wear isn't taxed much at all in lots of places and is more often diesel.