The timing for those factors doesn’t match the timing of the fertility decline in the US.

Birth control usage is slightly down since the mid 90s. Among sexually active women not trying to get pregnant, the rate has been flat since 2002. https://www.guttmacher.org/fact-sheet/contraceptive-use-unit...

Women’s labor force participation rate peaked in the late 90s. https://fred.stlouisfed.org/series/LNS11300002

It’s hard to see how a stronger social safety net would decrease birth rates, but that has actually also decreased, e.g. from welfare reforms in 1996.

Meanwhile, total fertility is down ~20% over the ~30 year period since then.