why do people automatically assume an idol is straight bc he talked about liking a girl once?

other sexualities like bisexual and etc exist. why do people always errase that? do you think if a male idol liked a boy before he’d say it out loud when a lot of their fanbase consists of heterosexual women who daydream about becoming an idol’s girlfriend? straight is not the only sexuality in the world. i think the fans just want their idol to be straight it’s weird