The US system is more complex, but I wouldn't attribute this to malice.
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).