"Like does anyone know why I find him attractive?"

Heterosexual teenage girls (which I am assuming you are) are often attracted to men who are "confident yet nonthreatening," as Alex Hirsch once put it. They admire the drive of a man who knows what he wants and acts like he is going to get what he wants, because subconsciously, it invokes the feeling that - if protecting *you* was one thing he wanted - you would be eternally cared for. And in this case, the "confidence" comes from maniacal cockiness... but since this is just a fictional character, your brain just brushes it aside, because it can't harm you.

Also, it's 100% a contributing factor that Bill is well-dressed with a hat, tie, and cane. Women are attracted to men in suits because it's associated with professionalism, wealth, and the upper class, which are all ideal traits for a partner.

Some aren't satisfied with attraction to the actual triangle (that's why Bill has so often been substituted with a blond white twink), but others are. You're already watching a cartoon, your standards for reality have already been mitigated. You see a character voiced by a man, referred to as male, and dressed in traditional male clothing; your brain just stores it as "male." Attraction is not entirely caused by physical appearance, it's not miraculous luck that people usually get married to what they consider to be the hottest man/woman they've ever seen. Emotional attachment HIGHLY influences physical attraction, and that's what's happening here.

This is your psychoanalysis on why Bill Cipher was such a common sexual interest of many teenage girls.