This is more a discussion for/about various pagan religions in the west, but I welcome the perspective of others as well.
The internet has done much to spread knowledge of smaller religions, but how effective has it made these religions spread? Is there a “cap” to the growth of these religions?
I think that there very much is. While we have online communities, we have almost no communities in real life. It is lonely, and even Steven Dillon (who was one of the few prolific defenders of polytheism) says that that loneliness is one of the elements that led to his conversion to Christianity, though he does put the major emphasis on his religious experience.
We also tend to lack a unity in structure. So many online communities emphasize a big tent philosophy, welcoming people of every tradition. Even when you get more dedicated communities to a “single tradition”, often there is such a fear of gatekeeping that eclecticism becomes prominent to the point that there is still no real unity of belief and practice. Often you will find people new to a faith ask questions and be unable to get clear answers in the same way a new convert to Christianity, Islam, Shintoism, etc. might get. I have personally seen this cause many people to feel lost and ultimately give up.
The sad reality is that the communities we are building are not effective at having substantial growth, at keeping people in the religion, etc. Gatekeeping is not a bad word, having a stricter structure does not mean imposing a strict orthodoxy onto an orthopraxic religion (though scholarship increasingly suggests the ideas are less divorced from each other than many pagans would like to otherwise belief), etc.
People say that the issue is that we do not have temples to go to, but did Christianity only spread to places that already had churches? No, they met at people's homes until such a time a church could be established. If we wish to see real growth in our various faiths, we need to do the same. Have regular and consistent meetings, hosted either at parks, homes, etc. Stop being so big tent all the time and not be afraid to "gatekeep". Be able to help new people understand the religion and provide resources, hold discussions, etc.
If these are not implemented, then the various polytheistic faiths will slowly die out. Heathens, in various locations, have already been doing some of these things. I have been a guest at a Blot before, a guest to a group that regularly has them. It is thanks to practices like that that Heathenry has been growing. Other faiths under the umbrella need to start doing the same.