This is a naive way of thinking, because a story serves a purpose, it's told for a reason and everything is introduced for said reason and keeping in mind the iro context of what's happening in the world. America would censor tower related stuff right after 9/11. It's a dumb example, but stories are told keeping in mind what happens in the real world when you tell them.
With this said, the real world is majority straight, and doesn't have the necessary awareness to assume otherwise from anyone, nor should they.
If someone isn't apparently gay, they're assumed straight, we can agree with this, right? With that said what representation does is showing us that other things do exist, it bursts the bubbles we might be inadvertently living inside, shows us new perspectives. If someone's gay but they're too ignorant to recognize it, learning about it through this could make him understand himself better. If someone is straight but narrowminded, this prevents it from happening ideally.
If you want something to be in a story, you have to say it in the story.