Being an activist as you have described can fill someone with adreneline and cortizol and a very strong sense of urgency and desire and even anger to get others motivated. The way you describe yourself feeling? Well, a lot of people don't have the mental strength or energy to get involved with a movement, and they can be afraid and also don't feel they can do anything about it or are only capable of just going along with their lives making efforts to ignore the challenges going on around them. Often the mindset is "someone else will do it, address it". That is what can happen in societies and human history shows that. It could be something that happens in human nature that has something to do with human survival.

splitimage is right, you are no good to the cause if you get burned out, and if activism is not getting any "true" results, the activists do get burn out.