First of all, it shows a ton of character growth. You can see them go through these different stages of their life and how they change through time. It means that they don't stay the same throughout the story, they are capable of making changes to themselves and how they view others. Character development is arguably one of the most important aspects of books. What better way to show off a characters growth than to change their views on things such as other people.
Second, it shows off the author's abilities to develop relationship. If the author can pull off the hate to love trope well, then it just makes you appreciate the authors writing abilities. They can shape these relationships into different things and when it works it's amazing. The hate to love trope is on the other end of the spectrum from instalove. You guys know how much I hate instalove, it's one of my biggest book no nos.
Third, it's entertaining as hell. The bickering, the fighting, as long as it doesn't go too far it's something that will no doubt keep me on the edge of my seat. Because hate to love relationships take so long to develop I am invested in their relationship longer than if they just get together right away. I tend to stop caring that much when the characters are already together and don't have to go through that initial trial period.
Fourth, it makes the characters more relatable, because there is no way that you've liked everyone you've ever met right away. You've probably been wrong about that sort of thing before. I know I have. The characters seem more down to earth if they don't just fall right into each others pants and "fall hopelessly in love" right off the bat. There is something rather endearing about two people having to face off the odds and eventually finding the other person was not who they thought they were, or they found that the other person was exactly who they thought they were but liked them anyway. Now while I do believe that sometimes books have to be a bit unrealistic as they are fiction, I do still love those small bits of relatability.
What are some of your thoughts on the hate to love trope?