In the wake of the COVID-19 pandemic, mothers in different-gender couples took on a disproportionate share of the increased childcare responsibilities. This was true even when mothers were working for pay, and even when mothers and their partners were both telecommuting (working from home). These arrangements have taken a serious toll on mothers’ employment and wellbeing. Thus, it is important to ask how two-parent, different-gender, dual-earner couples came to rely on mothers as the primary pandemic parents. We answer this question by combining data from a nationally representative survey of parents (N=2,016), fielded in December 2020, with in-depth interviews with mothers with men partners (N=73). In doing so, we find that the gendered structures of paid work that existed in the U.S. before the pandemic laid the groundwork for many families to lean on mothers by default during the pandemic, as well.