I think it began around my generation where the term "making love" was understood more to be "having sex." This makes some older songs sort of shocking to listen to, because of how they used and understood the term in the past. Books, poems, and so on from long ago seem scandalous in their setting.
Originally the term "making love" actually made more sense. It referred not to sexual activity, but to wooing, to sparking, to courting. It was what you did before you got physical in any way. It was the act of trying to generate love in your heart's desire, it was how you made love, literally. Now John Henley is right, you can't actually make someone love you.
You can make money, you can make good friends
You make mistakes and you can make amends
You can make it easy when push comes to shove but
You can't make love
-John Henley, "You Can't Make Love"
But you can make the situation and do the things which will tend to make someone who already likes you begin to love you. You cannot force someone to love, but you can craft the beginnings of love in the heart of someone if you do the right things, say the right things, and are the right person, to the right intended.
Making love was about saying poetry, taking her out to a picnic, seeing a film together, sitting and talking about your life and who they are, it was about all the things you do with someone to get them to love you. And that's about making love. It makes a lot more sense than how the term is used now.
Just bumping uglies someone might get them to declare love but you aren't actually making anything but babies - or perhaps a mistake. That's not making love its just sex.
Sex can be a beautiful and righteous demonstration of love, but it doesn't make love and the term has always seemed odd to me. But since its been used this way for decades now, when you read some old story about a man making love to a girl in a buggy on the way to the theater, you think they're doing the nasty and that's not what it meant at all.
And really, what this world needs is a lot more making love and lot less sex. It needs more effort to demonstrate you're worthy of your beloved and win her over than just trying to hook up or have a conquest.