I tried. Hearts stay
I disagree. Falling in love isn't always initiated by shameless flirting. Trust, care, being close, mutual understanding makes a heart flutter no less than a wink and a flirty tone
Well that's how the approval system works, right? It's not marked for the 1-2-3 options which is going to make them approve/disapprove but you have to either 1) think like they do and choose the option you think will make them like you or 2) answer honestly and hope they like it.
I think this is one of the reasons I really "fell in love" with Solas (both in game and out) because the way I naturally play (nice but also snarky) tends to get tons of approval from him. There are a bunch of hidden gems in his dialog for things that will gain his approval you might not realize if you don't choose the right one.
The hearts are just the really obvious "I want to flirt and make this a romance", which I think was a good approach game-wise. As others have said, it separates the "I just want to be a friend and compliment you" from the "I see this as a romantic thing" which is helpful in gameplay terms.
It's funny because,as a female, a lot of the heart options with Cass actually make her disapprove. Ah, Cass, such fun you are.