As much as we'd like to believe we have no biases, we do. Straight is the societal default. People who are not straight and just want to answer a question about their dinner run the risk of a bad reaction if the person they're talking to just happens to be homophobic.

Someone might prefer to get that reaction in a controlled setting, when they've emotionally prepared themselves for it, not during the course of answering a routine question about dinner. So that's why someone you're just starting to get to know might prefer to specifically tell you that they're gay, rather than waiting for it to just come up as an incidental fact during conversation.

This isn't about them assuming that you specifically care about their sexuality. It's about them being able to determine if you are a person with whom is safe to share details about their life... innocuous details that a straight person would take for granted as being safe to share.

Unfortunately, that doesn't mean there isn't any bigotry and associated violence against gays, lesbians, trans people etc. I wished that were true, alas here too we have our share of people who simply won't recognize reality. But I'm fairly sure that the people who are at risk of such violence here have their own ways of ensuring the chances of encountering people who are prone to acting on their bigotry in non-safe settings are reduced to a minimum, it's out in public where the risk is largest, and that increases as you get away from the larger population centers.

The bigger issue in 'coming out' here is to deal with such people in a family setting, that's where bigotry can and still does cause significant hardship.

If I would meet some stranger or some person in a work setting their sexuality would not be on my list of things I would be interested in, either we don't know each other that well or we have at best a working relationship, a job to get done, and to move the subject to sexuality would be - according to me - inappropriate.