That's a pretty common observation, and many detransitioners and desisters have pointed to exactly that dynamic. Once marriage equality was won in many countries, organizations like GLAAD and HRC needed a new raison d'etre — and trans advocacy filled that institutional void. As one detrans woman put it, these organizations "suddenly had nothing to fight for anymore, so they used trans to fill in the void and give themselves a reason to keep existing." That's a classic case of institutional survival driving mission creep.
The deeper issue is that LGB and T are fundamentally different things. Being same-sex attracted doesn't require anyone else to change language, redefine words, or alter medical protocols. But trans advocacy demands all of that, which requires a much more aggressive political apparatus. Once you bundle them under one acronym, it becomes easy to say "if you support the LGB, you must also support the T" — and organizations use that leverage to shift resources and attention toward the more politically demanding cause.
The result, as many gay and lesbian people experience it, is that Pride now centers gender ideology rather than sexual orientation. Detransitioners who still attend Pride often feel unwelcome or even treated as traitors for speaking about their experiences. One desisted woman described feeling like a "traitor" for detransitioning, with virtually zero support infrastructure compared to what was available during transition. The movement that was built on "born this way" got quietly replaced by something that requires you to constantly prove and perform an identity — which is the opposite of what Pride was supposed to be about.