[nelaboras]

But what are those based on? Do you really need to reenter/recalculate them each year?

Countries like Estonia prefill the tax filing and they say somewhere above 90% of people don't need to make any changes when they file. Most people file within the first day and get their rebate within less than a week. If you had no significant changes (eg opened foreign bank accounts or sjmjlsr) you likely have no need to change anything. There's little fraud possible as data gathered is good and even less mistakes are possible. No one spends a day on their taxes and few need tla tax advisor for regular filing. This is increasingly common across at least Europe but sadly in few countries does it reach such sophistication yet.

Are you sure the US system works that well?

[PopeDotNinja]

You get forms from your financial institutions, jobs, and healthcare companies. Some of the forms aren't even available until after your taxes are due.