Love songs

I wrote a musical about fifteen years ago - yes, a full length, two act musical. It has, of course, never been performed though it got close a few years ago when a composer named Dan Jones wrote a score for it. We still live in hope.
I wrote the story, the book and all the lyrics, most of them funny. But I had to write a love song and found it the most difficult thing to do. How was it that Irving Berlin, Cole Porter, Gershwin and others could manage it so well? What's the trick?
Maybe it's using ordinary, everyday language in a way that heightens it....
Here's a great one:

"If they asked me, I could write a book
About the way you walk and whisper and look.
I could write a preface
On how we met
So the world would never forget.

And the simple secret of the plot
Is just to tell you that I love you a lot,
And the world discovers
As my book ends
How to make two lovers
Of friends."

How can a dwarfish, quite ugly, predatory gay drunk like Lorenz Hart write such wonderful lines?
Another lyricist not as well known as Hart could turn out some wonderful poetic lines of love:
Mack Gordon, "the greatest impressionistic sketcher" according to Mark Stein.

"It seems like only yesterday
A small cafe, a crowded floor
And as we dance the night away
I hear you say forevermore
And then the song became a sigh
Forevermore became goodbye."

As they say on Masterchef "Wow!"