What's wrong with making someone gay or female for the sake of being that? That's a way to create depth for a character, and even if it doesn't add much to the story it helps bring a sense of liveliness to the world to give mundane details. Also, it seems that in your mind someone being straight or white or male or whatever is the default, so if someone decides to do forego that they're going to automatically get extra scrutiny and will either pass or fail the seemingly arbitrary test of whether or not this diversity is acceptable.
How is being straight or male any less deep? That's not a way to add depth to a character on the contrary it's a way to make a character feel shallow. If the reason they are there is due to race, orentaorien, or gender then by definition that is shallow and the character lacks depth because they're reason for being there is due to their orentaorien, gender or sex.
Depth to a character is added through conflict. And if the setting is right that conflict can be attributed to their race, gender, ethnicity or what ever else.
But putting a female character instead of a male character does not add depth to the character itself or the world, and the concept of that is ridiculous.