"Why are boobs attractive" produces a range of subjective answers. In fact, some people don't actually find boobs that attractive at all. You may have heard the phrase "He's more of a leg man". Well, that man finds legs more attractive than boobs.
That being said, there are some reasons why boobs are generally considered more attractive than fat on other areas of the body. Here's why.
Whether people are aware of it or not, certain aspects of the opposite sex are attractive to us due to our subconscious desire to reproduce.
Indeed, breasts can be attractive as they represent one part of fertility - the ability to produce milk - and therefore they're a natural attraction to many.
Of course, other parts of the female body also represent fertility, and are therefore considered attractive subconsciously too. A prime example of this is large hips, which represent the female's ability to bear children.
Other areas of fat simply don't represent fertility, and in some instances, highlight the opposite. Lots of excess waist fat can actually represent an inability to bear children if the female is very overweight.
Media
Another reason why boobs are attractive is because we're told they are by media outlets. Attention is drawn to boobs through different clothing styles, showing enough to remain attractive, while covering them enough to keep the imagination working smoothly.
Likewise, the media tells us that fat is generally not attractive. It's also a sign of poor health in many instances, and that's likely the main reason why fat is not generally considered attractive. That being said, there certainly are people who believe the opposite.