A deduction is a tax accounting device intended to distinguish income from revenue. In your hypothetical, why is any deduction necessary to properly compute income?

The fact that couples choose to have two spouses work is irrelevant. Daycare has no consumptive value either way. A company can choose to hire a separate CTO instead of combining the role into another position. They are entitled to deduct his salary anyway, and companies that don't hire a separate CTO can't complain about not getting a deduction too.