Why don't I pay my share of the associated VED if I was to take the bus every day? Or a taxi every day? I'm still polluting because of my journey after all. I'm being purposefully facetious here so apologies.
The thing is it used to be a tax to maintain the roads and many still think of it as so, but now it's a cash cow for the governments pot of black gold to spend on stillborn IT systems, Thomas The Tank Engine 2 and shady MEP's companies. While I'm having a whinge, the definition of excise is "a tax levied on certain goods and commodities produced or sold within a country and on licences granted for certain activities" - so where's that apply on a car I bought 8 years ago? Ah, the 'certain activities' part, the activity of using the roads, thus a road tax. It might not all be spent on the roads that's for sure.