Most people are not lgbt so why not market to that specific audience.
1. Because some artists care about more than producing lowest common determinator focus-tested-for-mass-appeal cash cows. And even cynical executives might see the value of a niche product that yields a deeply invested cult following that may be milked for more in the long run than yet another generic entry in an oversaturated market could.
2. Because most heterosexuals are not desperately starved of validation (or perhaps affirmation?) of their heterosexuality like you appear to be.
3. Because most people can empathise with characters not just over a commonality in such a broad and common aspect of attraction as being attracted to the opposite sex.
4. Because, since we are talking about merely including homosexuals, there are probably heterosexual characters that may appeal to their straight sensibilities.
(Far from complete, with some points I don’t think I can express well)
If I lived in Nigeria I would find it odd if a large percentage of people in entertainment were Asian or white.
Perhaps, but then, you are a presumably US-American chauvinist whose only perspective is that of living in the internationally culturally dominant country, probably consuming little if any foreign media, expecially not any that you recognise as such*…
* with the possibly exception of anime, with that weird weeb hatred of dubs, when everyone outside of the Anglosphere is watching dubbed Anglophone media all the fricking time…