Some gay men don’t pass as straight very well. They very feminine and openly present as a flaming homo. It’s not as simple as don’t ask don’t tell for them.
You also don’t realize when your straight how often sexuality comes up in casual talks. Not like sex stuff but like do you have a girlfriend, do you have any kids, are you trying to get married, that girl on my route is interested in you and asking about you, blah blah blah.
So it’s not really that simple even for guys who pass as straight but live openly gay and mind their own business.
The only people I’ve ever told at work I was gay is my union steward and my center manager at the time. The center manager because a supervisor I didn’t like was making ignorant statements around me and my steward because a coworker found out I was gay from outside of work and was making ignorant comments. I had the steward talk to him instead of filing a formal hr complaint against the harassment.