So much emotion and memory tied up in mother, the ones who gave birth to us and those who nurtured us, and then the full array of pregnancy-or-not/parenting-or-not experience of every woman... if you believe there's a Mommy War, well, Mother's Day is an annual battle. Brunch optional.
Ostensibly, every single one of these things should come up for Father's Day. For every mommy issue, there's a daddy issue. And the issues do come up, but with nowhere near the same volume.
The biological (and social and economic) opportunity costs are more visceral and obvious for women. And somehow motherhood is expected to be a primary identity, while fatherhood is somewhere on a list.
Or maybe the guys just don't feel the need to write about it as much.