You are thinking about this wrong. When you are in a situation where you take the standard dedication then you suddenly lose the benefit of doing any tax-deductible actions. So teachers across the board were immediately disincentivized from buying school supplies because it’s effectively not tax deductible anymore.

I rant about this all the time with charitable donations. Any behavior the government wants to incentivize through tax policy — charitable donations, student loan interest, IRA contributions should be credits that apply in addition to the standard deduction because otherwise there’s no incentive for most people.