"This isn't hard" -- as illustrated by both my and your mistake, this is as far from the truth as could be. Everything related to taxes is absurdly hard, whether it's setting up the right tax prep system, the right level of complexity in the tax law, or simply the right return to file as a taxpayer. My overarching point here is that Congress made a certain value judgment as to one of these very hard problems—that a healthy industry dedicated to getting people's tax returns correct might be in the best interests of both the government and taxpayers—and this might not actually be the product of corruption.
The fact is the vast majority of taxpayers do not have special situations, and it's straightforward to say "if you think you have any custom situation that may apply to you, file yourself".
And Intuit's behavior, as well documented in the ProPublica report, absolutely point to corruption and scammy behavior.
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.