Also: Even if they could, why would they? Grants are for research. Research only very indirectly affects their income. They could probably accept more students (so more tuition) if they would say to the faculty: no research, more teaching.
An uber driver who gets rich by other means will stop driving for uber, not drive for uber for free.
If the faculty itself is not willing to ask to spend the endowment on the research (and they know it most intimately), then why should the faculty ask the rest of us to pay?
An uber driver who gets rich by other means will stop driving for uber, not drive for uber for free.