They use little signs to signal others in their closeted community. The voice mannerism. Maybe a certain knowing glance. Things that may not be communicated in a still photo.
And while they will out their enemies, they still don’t like the possible outing from “just anybody” man or machine.
Given the high percentages of gays who are HIV+, and the expense of treatment, any company looking to lower their health costs would do well by excluding high-risk potential employees, while maintaining deniability of the real reason.