Why are there so few new popular religions?

Lots of new religions, just less focused on supernatural deities. Crypto maximalists are basically fundamentalists in a particular belief system. Even those who are loyally devout to a particular sports team are basically practicing a religion.

Is wokeism, and quanon not a new religion? I think we just aren’t seeing the religions that are forming or calling them such

In the U.S. I think "bible based" churches have scratched that itch.

Cult scholars think that some of those groups are coercive, but "by grace alone" is a safety valve that means you can blow off anyone who says you are going to hell. If you don't like your church you can find another down the road or go to divinity school and start your own.

They broke into jail and killed the founder of the LDS. Look at

https://en.wikipedia.org/wiki/MOVE

You really get a lot of resistance when you start something new! This song expresses the sentiment:

https://www.youtube.com/watch?v=PXOgZXUzp3E&list=PLBDDC70B0C...

There is a lot of interest in eastern religions and paganism in the US, but for better and worse it is not organized or evangelical. I know people in a coven who have a policy that you don't talk about any workings you do (even though nothing they do is scandalous)

I hesitate to declare that society is more 'rational' than it used to be, but people today are vastly more likely to think that someone who hears voices, sees visions, and makes prophecies is actually suffering from schizophrenia rather than believing they are genuinely communicating with the divine. That being said, there are still plenty of cults and new age movements out there. But they never seem to reach critical mass and usually fade away after a few decades.

I also believe it's the case that people look towards established faiths, rather than brand new ones simply because the older faiths have much more to offer ideologically. Beyond mere survivorship bias, the longer a faith has been around, the more likely it is to have better apologia and ideological arguments in its favor.

Existing religions have inertia. Parents naturally indoctrinate their children, and certain religions like Christianity expend lots of resources to convert non-believers (missionaries, community outreach, etc.). Religions have the ability to adapt, through reform movements, to better match modern values. It's also very tough for new religions, as they often rely on claims of miracles. Nowadays with cameras etc. it's hard to believe anyone's claims of miracles. Even Christians are often skeptical when another Christian claims that some miracle occurred in the modern day.

Well, one thing is now we have video, photos, audio.

Can you imagine how different the Old and New Testaments would be in video/photo form! Extremely different. People get to use their imaginations with the old religions on what people sounded and looked like. Not to mention that there don't seem to be quite so many huge and amazing miracles since everyone started filming everything.

One element is probably that the of the function and utility of religious practice has been replaced by other entities in our society. For an example of this, see this interesting opinion piece in the NYT: https://www.nytimes.com/2021/03/05/opinion/influencers-glenn... (or https://archive.is/R2Hil to get around the paywall).

I'd say religions in general have been falling out of favor and are being replaced by science and secular support systems. (In contrast the environments when the big religions started)

I'd like to see some methods and numbers to back up those claims.

How do you measure religions? Scientology is pretty new and has grown pretty significantly since its inception.