just a heads up this is my opinion, but I have been in the mythical community for a very long time (almost 10 years) and have seen a lot of repeating patterns in terms of why the community seems to ebb and flow. However, I do think that the community as a whole is beginning to fade away. First, here are some normal reasons for why the community seems to have its ups and downs with activity:

1) School and Summer Break

There is no denying that a majority of the community is in school. Whether that's high school or middle school, the changing of the seasons and semesters seems to have a notable affect on the amount of new members as well as overall member activity.

2) Lack of Persistence

An influx of new people in the community is usually trademarked by a decline in activity after about a year, usually by people leaving the community. Typical cited reasons for why this happens is because they don't achieve the results they want as soon as they want, and give up. 

Coupled with those reasons for regular ebb and flow of community activity is a few signs I've noticed that the community as a whole is beginning to fade away. Here are a few:

1) Over-reliance on older (or otherwise "more knowledgeable") members

This is probably the one I've seen the most. New people in the community, regardless of age, will often end up finding a single source of information to base their beliefs off of, and those beliefs become cemented. Usually this source is a person or website. I find this leads to a distinct lack of ability for nonhumans to be able to research their own information and draw their own conclusions. Add in the fact that a lot of older members who were heralded as information sources are starting to leave the greater community, and you end up with a lot of people who want a "mentor" and will tend to follow anyone they perceive as being more knowledgeable. Other things that I've noticed when people rely too much on one source of information is an imbalanced power dynamic within groups, a distinct lack of critical thinking, and inability to question their own beliefs in a healthy way.

2) Toxicity in the community

There's no denying that any community can become toxic under the right conditions. However, with the current state of the internet being what it is, it's very easy for people in a mostly secretive community to become toxic due to conflicting beliefs between different subgroups. Add in the fact that mental illness is pretty prevalent and that a lot of people are fairly young, and it's incredibly easy for people to be shitty to each other without really realizing how their actions impact other people and the community at large.

3) Echo Chamber Subgroups

An echo chamber in this case is a community where everyone more or less believes the same thing and reinforces the same beliefs to one another, and alternative ideas are not considered. Now, not every single nonhuman group is an echo chamber. But, it's easy for communities to get this way. It makes it harder for new members to not get scared away, makes people scared to ask questions, and in certain situations can lead to a totally stagnant community because nobody is presenting any new ideas, or new ideas get immediately shot down.

4) Lack of Interest/Alternative Forms of Escapism

I don't think anyone really wants to say this, but a lot of why the community started is, no doubt, because of escapism. People want to escape from everyday life, especially if your particular life situation is unhappy. Some people choose video games, movies, etc. But with the rise of reality shifting and similar concepts, it seems to be a better alternative to most people than trying to pursue the path of being nonhuman. People generally are no longer interested in it, especially since alternate forms of escapism are considered more socially acceptable.

Before people start panicking about the nonhuman community becoming completely dead, I don't think this is a bad thing. When you're in a community this long, it's very easy to feel like it's become your entire life. A lot of methods for achieving a physical nonhuman form seem to actually require that you make your life center around nonhumanity. But, perhaps with the lack of large active communities, it will become easier to find your own path rather than being dependent on other people. I will admit that it's nice to have a place to fit in, but that doesn't have to be in a large community.