This is exactly it. It's why GLAAD continues to talk year after year about how visibility is key towards making progress with LGBTQ issues and acceptance. Same as it is with any other marginalized group. You think most people were talking about starving kids in Africa before some white women started singing about them on TV? It's hard for people to care deeply about any issue they have no connection to or just can't relate to. Creating/reading threads on ERA isnt as effective as regularly interacting with Trans people in every day life.Because trans people quite literally exist within the margins of society.
People have female family and friends, they either have, or are close to people who have kids who are potential victims of a shooting, and whilst it's trickier with race, most people work with minorities or at least see and interact with them in their day to day lives.
What that means is that the persecution of any of those groups is real and confronting.
By contrast the trans community is so small and relatively invisible. Add to that the fact that being born black or female is something people understand whereas many people still have difficulty wrapping their head around being transgender.
It's harder to relate to and thus care about for many.
And with regards to ERA specifically, the number of people who feel comfortable or are knowledgeable enough to speak on certain topics can vary immensely. The trans community is a small one, even on ERA. Take away from that the number of people who are not willing to get in lengthy discussions with people in multiple threads, the number of people who choose to stick to just one or two social issues, the number of people put off by the handful of trans advocates who have a history of being extremely combative, etc etc. There are a lot of factors to consider first before accusing ERA liberals of ignoring or downplaying trans issues.