I'd argue it's the opposite. Early employees often have an outsized impact on the trajectory of a company and get it to a point where additional hiring is possible. Future generations of workers tend to iterate on the existing (unless there's a significant pivot) and come on board in a more de-risked situation often with salaries much closer to market.
Most start-ups also present equity as a form of compensation for work performed (trading cash for illiquid options). To take away that earned and vested compensation component because an employee doesn't have the money to exercise within the 90 day is not only arbitrarily absurd but also grossly unfair in my opinion.