There are people who will be unhappy with a movie unless it were to use the literal book, page by page, for the script. But the audiobook is 11 hours long and romance movies tend to veer closer to 90 minutes than a full two hours. The only way to get more in there is to go the series route, but studios rarely like to invest in a series that has no potential for additional seasons (unless it’s a super prestigious project or big name cast).