If we say that 10% of all people are gay, it should stand to reason that it complicates the dating scene. No gay person, male or female, can walk over to a person of the same-sex and start flirting. Straight people are offended if you ask them whether they are gay or not. That makes it difficult to know who you can date or be interested in. That might be the biggest reason why there are places like gay clubs, bars, and hangouts. At least at these places you are safe to make your interest known.
Straight people often make the mistake of thinking that you can see whether a person is straight or gay. That is only true about the feminine gay men and the butch lesbians, and even then you could make a big mistake – there are many feminine looking straight gays, and butch looking straight ladies. Even with the strongest gaydar, you can make a serious mistake, and in many cases it is a dangerous mistake to make. A straight guy can easily put your lights out if you are mistaking him for a gay guy.