I don't think it's because marriage is old-fashioned and outdated. I think attitudes toward marriage have shifted in a very bad way. Marriage use to be a meaningful commitment. Now, it's taken as lightly as the next one night stand. People look at marriage as disposable and go into it with the attitude of "well, if it doesn't work out, I'll just get a divorce". This is the reason I haven't married yet. I take the commitment too seriously to marry just anyone.