Why married men tend to behave better

I was dimly aware of this: "Researchers have long argued that marriage generally reduces illegal and aggressive behaviors in men. It remained unclear, however, if that association was a function of matrimony itself or whether less 'antisocial' men were simply more likely to get married."

A good example of a proper question being developed out of the results of some research. I'd also want to add my question: whether legal marriage only produces these results or whether other kinds of 'household' partnership do this.

Anyway, with regard to the question as put (rather than mine), it seems that it is not either/or but both/and.

As to my question, there is one bit that seems to be tangential to it, at least. "Burt said her finding may differ from past studies because marital rates have declined significantly in recent years, whereas marriage was more of the norm in the 1950s, meaning selection likely wasn't much of a factor.

It seems that marriage 'proper' is what was studied, so no figures would be available, I would assume, to answer my question. Both the research as reported and as it would have to be to answer my question seem to be crying out for an explanatory hypothesis. What do you reckon would explain the phenomenon?

Anyway, it does seem to me that the 'why' in the title still remains to be substantiated. Without an explanatory hypothesis, it can't be.
Why married men tend to behave better