And most of the common items are known to the IRS... mortgage and mortgage interest, property taxes, state taxes, education credits, retirement savings.
Common items that could be known to the IRS (but aren't necessarily today)... charitable giving, medical expenses, self-employed healthcare premiums.
The IRS could, relatively easily, email/SMS/snail-mail you a pre-filled tax return with the info they do have. If nothing needs updated, you just (e-)sign and provide payment info.
That not everyone agrees that it is a waste, or that society would find a better use for it is of course going to be a matter of opinion. Which some folks are heavily incentivized to weigh in on (to the point it may be a large percentage or all of their net worth), and to others it’s $50/yr.
Sure, but that's a tiny fraction of the population. Nobody is saying the IRS should send you a fixed return. Only that they should send what they have, and if nothing needs changed, great, society is better off.
In any case, most Americans do not care about this. I'm getting tired of the "10% of taxpayers couldn't fully use this system, so let's not bother" type arguments.
Certainly stock grants end up as W-2 income, but unless you automatically sell all of them, your choice of accounting methods matters. Many people I know have at least 2, one for employment-related stock and the other for their own trading. You don't even need options to get an accounting problem.
Also, I think you have a very narrow view of who actually cares about special tax circumstances. Teachers have several special credits. So do students. So do people who save for retirement. Not to mention people who run a small business or a side hustle. This isn't a 10% situation, this is more like 30-50% in any given year, and almost nobody files a bog-standard return every year for their entire life.
It would be nice, however, if the IRS told you about all of the W-2s and 1099s they got before you had to file your taxes. The good news is that you can do this if you file for an extension on your taxes and check an obscure section of the IRS website - many accountants do it.
I'm in the UK and there's reporting systems for- employers, pension schemes, savings accounts, charities and student loans- all to avoid most people having to fill in a tax return. Something like deducting sales tax would never be passed as a law because it wouldn't be accessible to most people.
As an analogy, we can say that laundry will never be automated because the washing machine can't separate whites from colours, doesn't apply stain remover, doesn't remove the delicates when it transfers to the dryer, etc. All technically correct, but people stopped caring. People have a financial and emotional attachment to their tax loopholes though.