Draft registration is compulsory based on residency; registering someone in error has no consequences unless there is a draft, which seems unlikely (no draft since Vietnam, large differences in how the US carries out war since then). In the event of erroneous registration when there is an active draft, past procedure was to allow time to reply and object, including through court process, so an erroneous registration would hopefully not leas to erroneous compulsory military service and associated risks. Not registering has potentially life long consequences that you may not be able to fix after you age out of registration; moving responsibility off of young men and onto the government seems fair.
Voting has eligibility requirements (citizenship, felony status depending on jurisdiction of offense) and registering someone in error could induce them to vote while inelligible, which is a serious offense.
Automatic tax filing might be nice for easy situations, but there's lots of things the IRS doesn't know and can't realistically know. Like how much capital improvements did you do on your house, and maybe even how much did you pay for your house ... whenever the IRS doesn't know the cost basis, they helpfully assume it is zero and send you a big tax bill... Still for w-2 + 1099s with cost basis reported, it could be easier.
The US has no compulsory ID. Parents are not even required to register births; medical professionals are, though, and a lot of things become challenging without a birth certificate, so I imagine the vast majority of births are registered. It's only within the past few decades that children were registered with social security at birth, instead of later. My siblings and I were only registered when it became necessary to get a credit on my parents's taxes; my parents were registered when they began to seek employment.
> These things can be automatically reported at the time of purchase.
Eh, not really. In my previous house, I redid the master bath twice (because the first contractor did a bad job). They both qualified to increase my cost basis when they were done, but the first time no longer qualified after the second... That's theoretically trackable through some seriously invasive purchase recording, but realistically, not so much.
Citizenship is also trickier than it sounds. There's no full and complete register of US citizens to compare with. Better to have someone declare they are, and jail them if they vote and it turns out they aren't.
Voting has eligibility requirements (citizenship, felony status depending on jurisdiction of offense) and registering someone in error could induce them to vote while inelligible, which is a serious offense.
Automatic tax filing might be nice for easy situations, but there's lots of things the IRS doesn't know and can't realistically know. Like how much capital improvements did you do on your house, and maybe even how much did you pay for your house ... whenever the IRS doesn't know the cost basis, they helpfully assume it is zero and send you a big tax bill... Still for w-2 + 1099s with cost basis reported, it could be easier.