First, ask yourself why the old system was the default and when those factors that caused the old system to be the default changed. The old system wouldn't persist across millennia and multiple cultures if it didn't, as a practical matter, work.

Second, I think your recitation of the state of affairs was overly-cynical and so you missed the point. Marrying for love is not the historical norm because romantic love doesn't indicate success in a life that was fairly precarious. Romantic feelings for your partner were certainly a good thing, but marriage was more an extremely involved with each other business partnership. It was thought of in terms of: you were joining your life to this other person, and joining your families (at least to the extent that you might call on them for help but it'd be nice if they could work together e.g. raising a barn for the couple), and probably were subsistence farming together (so you were heavily reliant on each other's abilities in order to not starve), and rearing children together (who would take care of you when you were old). You need to pick someone who will be at least a minimum level of successful in life or you suffer and maybe die. Plus, your pool of potential partners is relatively small...people didn't travel and how many people of marriageable age were within a 1-day walk?

And divorce was very frowned upon in the Christian West. It was a very high-stakes decision that was very difficult to undo. Romantic love was not a factor that would make this a success or not, plus it was common that most couples would grow to love each other at least somewhat over time (Ned and Catelyn Stark in the book of A Game of Thrones is a good example, though obviously fictional and nobility), so romantic love was basically a non-factor.

So, you see older-and-wiser people basically making the decision by arranging marriages because they were making the best decision for those children in light of the likely consequences for making a bad decision. And you see things like older men marrying younger women because the man has proven he's successful enough, removing the risk for her. While she would be young enough that her risks in childbirth were (relatively) low and her energy and ability to care for a large (remember: farming) family were high, removing risk for him. It's not about exploitation but about reducing risk (though, of course, people are terrible and so you do see examples of exploitation).

For romantic love to be a dominant factor, you need to see the consequences of a bad choice of partner somehow be lessened or disappear. Or, put another way, you need to see a system with romantic love making at least as good a choice for.the couple as the old system. When and what those factors exactly were depends on the culture, time period, etc., and are something you can research, but there's a reason it correlates with industrialization.