Most of your other examples aren't really valid because the vast majority of people take the standard deduction anyway, so things like charitable contributions, home energy deductions etc. don't matter.
But most importantly, the whole proposal always leaves the "You're welcome to do your own taxes if you have anything we haven't addressed." It's just that Intuit didn't want to even allow this option because they know the vast majority of people don't have complicating factors, and they hadn't gotten really good at scamming "free filing!" users into buying upgrades they didn't need.
This isn't hard, and tons of other countries do this.