You made the sister into a far too interesting character. That was your mistake.I hear ya and everyone else that complains about it. I thought that people would at least be glad I've been open about this from the start instead of trying to pull the wool over everyone's eyes and then giving everyone a big surprise at the end. At least now everyone knows how the story is NOT going to end.
To use your sweet analogy, imagine living in a town where every store only sells candy. Sure, you like candy, but maybe every now and again, you want something else. Maybe you want ice cream, or salad, or veal? When I started making this game, it seemed like every single game had more or less the same brother/sister love story plot. So I wanted to make something a little bit different. You can tell me that was a stupid decision and my game would be more successful if I told a more generic brother/sister love story, and you may be right, but that's not the direction I wanted to go in.
She's not the best looking one (I dig Molly more, and there are others that look awesome) but she's simply too great a character to resist for most.
I've got a whole bunch of characters your game has me interested in, but even I would still like to see at least some optional route where you can go for your sis. Just because why wouldn't you want to pick a girl like that?
Or too use your anology: if you didn't want to sell candy, maybe you shouldn't have made it so delicious.
Who knows, maybe after the game is done you'll add a sis route, just for those who prefer her.