Entrapment is a thing, but I'm not blaming marriage declining because men fear entrapment -- I mean, it's a valid fear, especially if the solution for a woman to get benefits is to be married (it'd be used as a tactic).
Marriage is a contract at its core. This contract now favours women to the point where you'd be better off proverbially signing a loan with a loan shark. They can, and often do, "pull the cord" at any time, and they make off like bandits, even at "at fault" situations.
Child custody? Primarily awarded to mothers, even if she's a drugged up street-whore and the ex has a solid job, home, and his life together.
Alimony/spousal support? Yeah, there's a reason why people "joke" that a hitman is a lot cheaper than a divorce.
Hell, even if you cohabitate with a woman now and not marry her, she can still financially destroy you.
MGTOW may decline if all the bullshit, biased laws supporting women (e.g. in the courts, arresting procedures, et cetera) are shit-canned so there is actual equality, but MGTOW isn't going away.
It's a reaction to modern women's natures, and also men have taken it as a life philosophy (working hard, constantly improving yourself, bettering your situation and health, et cetera) to live by.
Unless you can completely change how modern women act (Christ, does this make me sound like some religious fundamentalist prude!), stripping away their sexist senses of entitlement? It's here to stay mainstream.