A restaurant charge is simple - here's what you ordered, here's what each thing costs, here's the total. If you really suspect shenanigans, you get a copy of the menu to validate against.
Property tax is usually pretty simple, as is vehicle registration. Both can be described in a couple of paragraphs.
The problem right now is that even if the forms were precalculated, the IRS doesn't necessarily know about the deductions you're entitled to, and claiming those is a far more intricate process than simply filling out your PII (1040) or your wage info (W2).
Here's a relevant example. I just started going to school again at the end of last year (November). A run through with TaxAct/HR Block showed me as owing about $600 before any deductions or credits - you have to tell them about those. The fact that I started going to school gave me the "lifetime education credit", and turned a $600 payment (that I could not afford at the time, and was somewhat stressed about) into a roughly $2K payday.
Without the software, or paying an accountant, I wouldn't have known about that, and paid $600 that I didn't need to pay.
The lifetime education credit is calculated based on the 1098-T that your school had to file with the IRS.
I had to help two friends navigate TurboTax after they couldn't figure out where to enter a 1098-E (student loan interest), so my anecdotal evidence is that TurboTax easily misses certain items when hey ask "Did you go to school this year", but not "Did you have education expenses" (or something similar). Without someone who had already used the software to enter similar items, they may not have been able to get that credit.
My main complaint with TurboTax (other than the fact that I have to use software to file taxes and buy a new version every year) is that I am charged to e-file at the state level.
This is what I mean. Comparing income tax filing (with a W2 and a 1040 by mail, with nothing else, that's at least 3-4 pages of work, with no guarantee that you're paying what you ought to be) with a restaurant bill (an itemized receipt of things you bought) is fundamentally dishonest.
Every comparison made is against single charge, a single payment, based on a usually simple formula, rather than an entire freaking body of law.
Is it a 'conflict of interest' for restaurant to both collect money for my bill and tell me how much my bill is? No. The rules are clear so anyone can audit their own bill if they feel they're being cheated.
If the government just said "You owe $673.25" and wouldn't tell you why or how they got to that number, then I would see a conflict.