"Many poorer and less educated Americans are opting not to get married at all. . . . Marriage is becoming a more durable, but far more exclusive, institution." How is it exclusive if it is by choice?
I think they are referring to people excluding potential partners due to their lack of money or education. But I agree, their writing insinuates the institution itself is discriminating.
Two poor people can be really hurt by the way marriage is set up. Benefits get weird. The income might put them over the threshold for receiving benefits. And if the marriage goes badly - for example, if a spouse winds up being abusive, develops a drinking problem, and things of that sort - the poor person is stuck in the marriage simply for not being able to afford a divorce.
It isn't just that, but marriage costs time and money. It varies by state and county - and the services the courthouse offers varies as well. If you cannot afford the initial fees, the entire institution is off-limits.