Personally, my thoughts on this issue are mixed. Clearly Mitcham wants to be out. He wants his relationship to be publicly known. I'm cool with all of that. If NBC made a conscious decision to not include his sexual minority status, that is one thing. It could either be outright homophobia on the part of the producers of the broadcast, or it could have been a simple business decision made based on the demographics of their viewers.
When it comes to Mitcham's partner, there is a bit of a sticky situation. While other athlete's wives get coverage, typically girlfriends do not. So perhaps their unmarried status played a part in the decision not to cover Lachlan. We also have to consider what Mitcham might or might not have disclosed to the producers. Did he make it clear to them that he and Lachlan are in a committed, long-term relation ship? Or did he only mention Lachlan casually to them, which might leave them thinking that Lachlan is no more than "flavor of the month" type thing?
Who knows for sure?