That’s an oversimplification. For example, how do you expect your home government to know about incomes/dividends/gains that you earned in other countries. And that’s just one example.
It's just that in the US, companies like Intuit lobby to keep the tax code as complicated as possible so they can sell tax filing software.
Americans have grown up with complicated tax codes, so that's all they know. They don't realize it can be better.
Your employer reports your income to the tax authority.
They send you a tax assessment, including any reliefs they think you are eligible for. If it's correct, you just pay the amount.
Otherwise you can file an objection. But for the majority of people, the assessment is correct.
If you have additional income, dividends, gains and under certain other circumstance, you're liable to fill out a tax return (self-assessment as it's called). It's a very simple form that contains information that applies to the vast majority of those who need to do their self-assessment. After you've sent it back, they'll calculate if you've overpaid (and compensate) or underpaid (and require you to pay what you owe) or neither. It is trust based but they do audits up to 7 years back, and if have lied or made mistakes, then you'll be liable.
The few richest of the richest who fall outside the above two (they still need to do a self-assessment) probably have a completely different process but it doesn't matter because they have the resources to hire firms to figure it out.
how was that hard to figure out
And someone working minimum wage with no overseas dividend income must manually read every space for these “missing” line items?
Seems like you’re wasting the minimum wage worker’s time.
[1] https://en.wikipedia.org/wiki/Foreign_Account_Tax_Compliance...
There is a ton of information sharing between financial institutions and governments.
It is not just FACTA (though that particular law takes things much too far)