That has declined as people came to understand that being gay, lesbian, bi is part of how a person is made. Under public pressure, a gay person can act straight or at least act not gay. But it doesn't change who they are, doesn't help anyone around them, and makes them miserable. There is no point to it. Thankfully popular opinion and the law have adjusted to that reality.
Being transgender is the same way. A transgender person is not someone who dresses a certain way, takes hormones, or gets surgery. A transgender person is someone who is absolutely miserable when they are not permitted to express the gender they feel. It is part of who they are deep inside, how they feel every day of their life. Like gay people, they can hide it to avoid abuse. Like gay people, it's not fair to force them to do so. And it doesn't help anyone around them either.
Unfortunately, this gives the movement a bad reputation. Some prigs aren't lgbt people at all, but they speak on behalf of them, as they also speak on behalf of other groups that they aren't a part of. Some prigs might actually be a part of the minority they speak for, but I would hazard a guess, based on no data, and say that these are the minority of all prigs.
I think PG's problem is with the prigs, not the lgbt movement itself. Can these be separated?