Not an US citizen. And in my country tax returns are certainly easier than the US. And our country also have a system in which people below certain money can just go to the tax agency and a government employee will do your tax return for you. But it cannot be fully automated, as the government doesn’t actually know 100% what do you own.
When they send you letters after asking for things is for you to give them paper documentation on why you deducted some things, or because they are inspecting some things a your deduction raised a flag. But it’s not like they just know precisely how much everyone should pay. If it were that easy tax returns would not be a thing as it is in most of the world.