I married for love ~ definitely ~ but also, I think, because it was the respectable thing to do. I wouldn't have dreamed of 'living in sin' ~ as it was then called.
Things are different now. No-one seems to care much any more, whether co-habitating couples are married or not, so they need to have other reasons to marry.
I think that financial security, under the law, is an important one ~ should the relationship fail, that is.
I am not saying that love isn't important in a long-term, committed relationship, I'm just wondering if marriage is. Do people really need a piece of paper, to say that they love each other, and want to stay together for life? ~ No. I don't think that they do.
So, why marry then?
Financial and social security, for the two partners and for their children, I'd say.
Also, religious and cultural reasons may come into it.
And the actual special marriage ritual, with family & friends gathering in celebration are important.
Marrying for love is a lovely romantic idea and I'm still all for it, but I don't think that it is necessary, when considering why one should marry, as co-habiting without a certificate covers that, which is probably why not much was made of it on the programme you heard.