Notice how most of your points are just physical traits, and ocean and skateboarding are practically the only things you can name that she likes. Physical attraction can be a powerful thing but it's not enough to make a relationship work. Marco and Jackie have nowhere near as much chemistry as Star and him, which has been building up since day one. Whereas throughout all these years Marco couldn't even speak to his lifelong crush, and when he finally could he still didn't learn anything about her because he would't even let her answer the questions before moving on to the next ones (because he is such a nervous mess).
Also, Star is just a late bloomer, she'll develop a body one day - granted, not as hot as Jackie's, but still. She's very fit as well. More importantly, the best thing about Star is that she is Star. Y'all Jarcofags like to pretend that she is a total bitch, but she and Marco actually deeply care about each other and you know it. Marco doesn't need a reason to love Star because he alreasy does, even if it's only platonic so far. It wouldn't take much for it to grow into something else. Besides, being the King of Mewni must come with some good perks.