Why don't they though?
Because they are beta males who have had the stuffing knocked out of them and know they are no longer marriageable because they are no longer young and attractive and have had their earning power crippled by divorce. They don't even want to have a relationship with a woman, let alone remarry, and so cannot be expected to defend marriage.
It is more lucrative to bitch like women as MGTOW on their YouTube channel rather than have a practical solution to this problem. Beta males are not leaders and have, like women, only the power to withhold. Being mostly atheists, these beta male victims of feminism don't care about what happens to their civilisation even if they have sons. Proposing a practical solution like abolishing no fault divorce would be boring and unprofitable in terms of YouTube likes.
Basically, they are men so embittered by their experience of women they don't want to have anything to do with one again, not even hire a prostitute.