Many people may not think it is their place to speak. Some people may think they wouldn't be the best person to advocate. Others might think other people speak better about it. Other people might not be in a position to speak about it.
In the UK we have many people who claim to talk for the "working class" that as one of my friends put it "looked like they have never done a day of heavy lifting in their life". I wouldn't speak on behalf of the working class, I do a white collar job.
> From my perspective opting out means no change. And no change means structures stay the same. Therefore, they persist and are maintained with your (weak) approval.
Does it? Many structures fall in under their own weight, many organisation reform from within. You are assuming the world and people within them around doesn't ever change. There is a whole bunch of assumptions you are making. Sometimes the best thing you can do is to do nothing.
I used to cycle to work every day. That was more effective to get my coworkers cycling in than any amount of advocacy I may have done verbally. Just yourself being the change you want in the world is sometimes sufficient.