Government wants you to either ride the public transportation system or buy a new car so that they get the tax revenue. The government makes far less revenue from those of us that preserve a vintage vehicle and use it for commuting.
I think their motivation is actually different. I don't think vehicle taxes are a cash cow because the necessary outflow, for road maintenance and such, is huge.
I think the motivation, maybe even subconsciously, is the desire to have as many modern vehicles on the road as possible. And it even makes some kind of sense. In a narrow minded sort of way.
Picture a world of cars that communicate with each other. Throw in the Google self-driving cars, too. These vehicles might make traffic more easy to bear and more safe.
But if there's a bunch of 1986 Plymouth Reliants mixed in, then that's going to cause some trouble.
It's not just our 'leaders', but our very neighbors who want to tell you that you can't drive that beat up vehicle. You must buy a new one.
I call it narrow minded and short sighted because so much new technology and so much disdain for simpler transportation would be unnecessary if people would just get over the notion that they must, must, must (!) drive, drive drive.