Simple: anti-discrimination laws only apply if you're being discriminated on the basis of being in a protected class. being gay is a protected class. Being ICE isn't.
In some jurisdictions being gay is a protected class, in others it is not. Even the USSC ruling today doesn’t create a new protected class; it simply (and correctly) determines that discrimination based on gender nonconformity (whether sexual orientation, gender identity, or other) is discrimination based on sex, which is already a protected class.