Bridges did so well not because it was a forbidden romance, but because it appealed to aging viewers. Same with the book. Eastwood was 65 at the time of release. While Streep was much younger, her character was meant to be in her late 40s...neither spring chickens in life or fiction. But they appealed to many 'love second time around' viewers which is the opposite of traditional romances for younger viewer.

The romantic story was somewhat slow burning, but the end of the film was a real tinderbox of emotion.

Some side notes relating to this film...

There are two Kincaid trucks. After filming, one went to a museum dedicated to movie vehicles. The other became a workhorse on Eastwood's hotel in Carmel-by-the-Sea, California...where he lives and filmed Play Misty For Me. Of course, the truck was a popular photo op for visitors and guests. (guests in the hotel may also find some film props in the rooms...)

Also, at the time of filming, Eastwood was coming to the end of his relationship with actress Frances Fisher who was pregnant with Eastwood's 7th child. She was named Francesca after Streep's character in Bridges.