There was Red Stone, Atlas, titan, Saturn I, Ib, and V. Mercury, Gemini, and Apollo. multiple contractors at each phase.
Instead we have multiple moonshots, bringing diverse approaches, and constrained by a budget. Since we know from Apollo that “if money were no object”, we can do this, it’s a good approach.
The reason we never moved on from Apollo is because economics matter. We were able to beat the tyranny of the rocket equation; now we are seeing if we can do it for a much smaller amount. And we have multiple bets on different approaches.