What factor caused the reliance on Soyuz for US astronauts to diminish significantly after a specific program's success?

The successful commercial crew program operated by American companies, which reintroduced domestic crew launch capability for NASA.

The dynamic of dependency on the Soyuz system fundamentally changed with the operational success of the commercial crew program spearheaded by American private sector companies, such as SpaceX. This reintroduced the capability for NASA to launch its astronauts on domestic hardware. Prior to this, US astronauts frequently launched on Soyuz rockets simply because there were no other immediate options available to sustain the required crew rotation schedules on the ISS, a necessity that involved significant financial arrangements for NASA over nearly a decade.