How are they pulling up the ladder behind them?

At this point, services delivering payloads to space are scarcer than payloads themsleves. Launch service contracts from them are already essentially unavailable. Running ahead while Blue Origin and Rocket Lab still catch up is a significant strategic advantage.

Hot payloads for the next few years are network connectivity and compute, two verticals SpaceX has chosen to compete in, which are major sources of revenue. Aside from saving room for strategic relationships with the US government, they can easily utilize all available capacity themselves.

If (1) SpaceX is the only organization actually able to launch at scale (vs. promising eventual launching at scale while burning through $billions), (2) the Big Money in space will be made with large constellations of internet/cellular communications satellites and orbital DC's, and (3) SpaceX is winding down the launch services that it provides to outside customers - then all of SpaceX's competition for the $$$ will be stuck on the ground, giving them a monopoly.

Eventually, anti-trust law and/or another competent launch provider might break that monopoly. But Elon's buddy Don will control the Justice Dept. for a couple more years. And even for the competent, ramping up launch is slow.