This was not a convention for only gay people. Everyone was invited. If you want to make a convention that's aimed at straight people "to even things out", go ahead.
OH WAIT that's already every convention ever.
I wouldn't say that conventions are aimed solely at "straight people" rather at the main demographic.
Whatever demographic constitutes the main consumer of what the business sells will obviously be where the most attention is directed at.
It seems that white, straight people between their late teens and mid 30's buy the majority of games.
I would say that things are not aimed at a certain sections of the population with the intention of being exclusionary to others but rather business goes after where the money is.
Games aimed at gay people and other minorities would I suppose from a business sense be considered "niche" and not massive profit driving markets.
Unfortunately I hazard a guess and say most gamers would not be interested in devs making an effort to include gay / minority figures / scenarios etc in games as they have no affiliation / relationship with those issues and perspectives.
In a way I suppose the only way for gay people and minorities to see products that contain anything relating to themselves is for products to be created and marketed solely for their consumption, rather than finding anything they can relate to filtering into general, mass market products.
This convention is a reflection of that.