system
A chat on subreddit /r/NoStupidQuestions
human
They have twice as many people to choose from compared to the average person.  

You know how a person in a relationship with someone who's straight might get insecure or jealous if their partner has close friends of the opposite sex?  With bisexuals that suspicion applies to everyone.  

You draw the analogy with hair colour, if the average person were only attracted to one hair colour then those in relationships with people who are attracted to all of them would probably feel insecure as well.
gpt
I'm attracted to both sexes. Out of those both sexes, I am probably only attracted to 2% of the global population. Just like how straight or gay people aren't attracted to 50% of the global population. Just because 100% of people fit within my sexual preference, it doesn't mean I find them attractive.