Because the money would not be spent on any of those things. Buybacks are a favorite boogeyman, but they are just tax efficient dividends. They certainly give people something to complain about though.
"Tax-efficient" is weasel language. If the money was spent as dividends it would be taxed and then would benefit someone besides the executive suite and investors. If they were unwilling to pay that tax, then the money would need to be reinvested in the company in the form of higher salaries or R&D. So yes, if buybacks were illegal the money WOULD go to one of these things.
The potentially taxable dollars are the same (non-withstanding the buyback excise tax), it's just shaped differently.