For the most part it's nothing to do with more men GTOW and realising the vindictive nature of women, but rather because women in Western countries are becoming wealthier and have better jobs than men on average, as a result of feminism and government policies actively favouring women.

For the vast majority of women marriage is simply a means of obtaining wealth and living an easy life, which is why women almost always marry men who are wealthier than they are.

However these days there are increasingly few men who are wealthier than the average woman, and the gap between men and women in terms of earnings is only going to get wider and wider as the years go on, in women's favour.

Basically, women these days really don't "need no man". They have the potential to get much better jobs and earn significantly more money than the average man any way, and failing that there's always the government they can leech off too.

I think women are increasingly see marriage as a bad deal for themselves as well. They realise that they can obtain far more money taking advantage of feminism and pro-women policies than they can marrying some average man who probably earns less than they potentially could and also not getting married allows them to act totally uninhibited as well.

There's a view on MGTOW that the decline in marriage is being lead mostly by men, but I think it's actually women who are leading the decline in marriage.