Or maybe is because of politics.

https://www.refinery29.com/en-us/2021/03/10386020/republican-men-against-covid-vaccine-anti-vaxxers

IT seems that most anti-vaxxers are men. And they would go on a rant about how you can't take away their freedom. Not just that, they specifically say "my body, my choice". All while denying that to women. XD

Maybe the answer to your question is, how can you persuade more men to want to be vaccinated.