Because it couldn't possibly be more complex and attributable to other causes like, oh I don't know, kicking fathers out of their children's lives (with statistics from the US Census openly stating most all custodial parents are mothers and proportions are statistically unchanged over the years)?

"In the spring of 2002, an estimated 13.4 million parents had custody of 21.5 million children under 21 years of age whose other parent lived somewhere else. About 5 of every 6 custodial parents were mothers (84.4 percent) and 1 in 6 were fathers (15.6 percent), proportions statistically unchanged since 1994 (Table A)." [1]

"Custodial parents have become more likely to be fathers over the past 24 years, increasing from 16.0 percent in 1994 to 20.1 percent in 2018...

The number of custodial parents has varied somewhat over the past 24 years, including the proportion of fathers who are custodial parents. In 1994, about 1 of every 6 custodial parents were fathers (16.0 percent). By 2018, that proportion reached 1 in 5 (20.1 percent) (Appendix Table 2)." [2]

[1] https://web.archive.org/web/20211212183149/https://www.censu...

[2] https://www.census.gov/content/dam/Census/library/publicatio...