It is not primitive, it is intentionally complex and riddled with loop holes so it can be manipulate by those who know how to creating all kinds of new markets for law, filing, and enforcement.
The reason why it's so easy to file taxes in lots of European countries is because the tax system (for the general population) is a lot simpler. For example in Austria you pay the same amount of taxes no matter if you're single or married, capital gains are taxed at a flat rate and directly withheld by brokers, and "social benefits" are typically handled outside of the tax system instead of being folded into the tax system.
In the United States the tax code is a lot more complex. You pay different taxes if you're married compared to if you're single, capital gains tax rate depends on your other taxes so brokers can't automatically withhold taxes, and there are a lot of edge-cases for certain other situations that can't be easily automated. Like tax credits if you're affected by natural disasters, different tax handling for railroad worker pensions, and so on.
With that complexity it is a lot harder to automate taxes, but it's also hard to retroactively reduce that complexity, as any changes will negatively financially impact some of the affected groups. Also I think that it might be easier in the US to handle those aspects as part of the tax system (instead of handling them independently), as the federal government has the authority to collect taxes, but direct payments (outside of the tax system) to individual groups might be harder? (But I'm not sure if that's true).
what do you think OP was talking about? they are keeping it complex on purpose.
To me this looks somewhat like the broken windows fallacy: In countries where the tax code is simple and allow for "automated" taxes nobody is going to advocate for a new law if it makes filing taxes a lot more complicated. But in countries where the tax code is already complex adding one more complex law doesn't make too much of a difference.
https://www.propublica.org/article/inside-turbotax-20-year-f...
Part of the political resonance with the tax issue is the cost of doing taxes and the stress it causes. If the process was as simple as verifying a document, signing it and sending it back (or heaven forbid, docusigning it and clicking 'next') then the discussion changes to "what are my taxes doing?" and "is this worth it?"
I have a hard time seeing past malice, when some of the most high profile easy to target tax dodgers consistently pull it off with only good outcomes, or when the IRS is given more money to specifically target them yet doesn't.
The level of complexity in US tax code isn't outrageous, but there are a lot of exemptions. And most European countries have them as well.
The stonewalling of tax authorities sending me the bill, however, is pure malice.