I actually don't understand why the laws are written that way, apart from the political goal of causing W2 workers ("suckers") to bear a disproportionate tax burden. A W2 worker incurs expenses that are necessary to earn their income, including food, transportation, clothing, and healthcare. If they were able to account for these necessary expenses as a business does, the expenses would be directly deducted from income.
And that's not even getting into the S-corp self-employment-tax dodge.
For one, no, those expenses aren't deductible even if you do itemize. They're considered "personal expenses" even though they were necessary to earn that W-2 income. If you buy a car and use it at least 50% to get to 1099 client(s) you can deduct that portion of it (including accelerated depreciation). But if your income is coming from W-2 job(s), you simply cannot.
For two, the standard deduction is better seen as a personal exemption (which it subsumed), giving everyone a level of income that they don't have to pay tax on. Especially given that business expenses generally flow through as direct subtractions regardless of the standard deduction.
There is definitely tension between allowing deductions to account for actual income fairly, and the resulting (de facto) requirement that everyone do minutiae accounting for their personal finances.