These groups often refer to themselves as 'mommy groups'. Child care is something disproportionately shouldered by women here in the USA. I do not think this is just, I am not approving that fact, I do NOT assume that is the way it SHOULD be- it is simply a fact. In a civilized society men would share in the work of child rearing equally- but we don't live in that society.
Because of that disparity the pandemic saw a far larger drop in women in the workforce here than men- because they were the ones it fell on to take care of the children no longer attending school.

Again-I do not think this is fair, or an acceptable state of affairs- but it is the reality here.

IF there were a large number of 'parent groups' with the same focus as the 'mommy groups' with a 50-50 mix of genders, then they would be just as vulnerable and be targeted just as hard.

The 'mommy groups' were easy targets not because they were mostly women, but because they were parents, and in our society parenting and child care disproportionately falls on women.

This division of responsibilities is unfair and deeply damaging to society- but it is a reality just like racism is- a reality that should be fought against and changed, but pretending that reality doesn't have implications to how messages and propaganda are disseminated accomplishes nothing good.

This propaganda dynamic changed with the politicization of the pandemic and vaccine mandates- once that happened, and it was turned into a culture war, the anti-vaxxers now had an easily exploited way to appeal to a wider group- now an entire side of the political spectrum was primed to be vulnerable men and women alike. The prime route of entry no longer was those that had primary child care responsibilities, it was political affiliation- something that is more gender neutral in our society.

And the demographics of the anti-vax movement changed drastically over the course of a single year- compelling proof that men are just as vulnerable to targeted propaganda. According to polls last year women still are more likely to oppose vaccine mandates, but its essentially the same as the percentage of men that oppose the mandates.

Though the gender gap for universal vaccine mandates narrowed by 5 percentage points, women continue to be less supportive of requiring everyone to receive vaccines compared to men (63% to 67%).

That was from last fall, barely a statistically significant difference - I would bet money the difference has only narrowed since then. Quite possibly it has even reversed.