The US is special because the process of writing the tax code is corrupt. (Not uniquely corrupt, but certainly near an extreme among major countries.)
The US is also special because it has 50 states, all of which have their own thoughts about taxes.
But I don't have the articles at hand, and don't feel like an internet debate today, left as an exersize to the reader!
How would they know now?
These examples are silly, most people are not selling a car privately all the time and they can handle any reporting or changes when you transfer the ownership.
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That being said, my Dad worked for a few years at the IRS part-time before he finally retired. He loved it. (My Dad is one of those people who enjoys taxes and finds them soothing.) I concluded that the IRS is a white-collar make-work program. It also leaks a lot of confidential social information, because he got to see all kinds of tax returns from all slices of economic status.
For more complex cases where you have more deduction and income sources the government doesn't really know all the individual setups you may or may not qualify for and they only audit a small percentage of filers every year.
The reason it's been blocked is a mess of ideological and economic. Ideological from people who interested that want to make taxes more annoying so people are generally more anti tax and then they get elected and make cuts to the top percentages/businesses permanent while the tax cuts for the majority of citizens are temporary. This sets up a debt crisis when those 'temporary' cuts are also extended they can use to leverage for government cuts. On the economic side there's a huge amount of money made each year by preparing taxes for people too intimidated by the complexity to DIY it. So they ally with the generically antitax side to keep their business going.
[0] https://www.irs.gov/statistics/soi-tax-stats-tax-stats-at-a-...
https://www.irs.gov/businesses/small-businesses-self-employe...