A lot of more traditional hobby communities like HAM and model aircraft clubs, that want you to take a dozen tests to play with them. Those same communities seem to scratch their heads as to why they can't attract new members.
I found HAM folks super welcoming. I came to take the entry level test and they encouraged me to take the next level one at the same time, and generously offered to help me pass it.
Ham licenses make sense. If you screw up, you ruin things for everyone, so you have to make sure everyone who transmits knows what they're doing. The problem is the elitism, and how many of them look down on anything more modern than vacuum tubes as not being real amateur radios.
Right target, wrong reason: Testing for HAM makes complete sense. It's government imposed to get licensed, and that's because the equipment required for HAM could be easily modified to interfere with other electronics or run up against communications laws. HAM being self-regulated (in that everyone is a snitch if they find out you're operating without a license) is only going to be possible if everyone is a snitch. Also, everyone has to share the radio spectrum, so you should know how to be a good actor before you get the chance to go on air.
But there is gatekeeping in HAM in how few beginners focused resources there are. At least in Canada, I found only one set of books that taught the latest HAM exam and one series of YouTube videos (thanks Ylabs!)
I have found very few "your first radio" resources. Hunting for that sort of thing is an intimidating experience, full of jargon and acronyms (not stuff like "VHF" and stuff you need for the exam, but model descriptions and stuff). Lots of sites and radio club web pages aren't kept up to date, and it's a lot to ask of new people that they come out to field day for in person meetups when it's just a bunch of strangers.
I think those only need 1 test to play with them, and that's because they are regulated by the government. They want people to follow the rules because if they don't it can come down on all of them.
The biggest one of these that I know of is falconry which requires 1 falconry test, 1 hunt test, 1 inspection, and finding a two year sponsor. Falconry is specifically set up to gatekeep as to protect the sport in the USA.
Yeah, I have yet to encounter ham gatekeeping beyond "don't broadcast without a licence and callsign". The test itself is all important stuff, as I'm studying for it in Canada.
It's dead because what we're doing right here is an easier way to talk to people around the world. You have to be nerdy enough to love the technology for it's own sake, so that cuts down the pool pretty severely even before the cost and "red tape" come into it.
Falconry in the US exists as an exclusion from the Migratory Bird Treaty Act and Bald and Golden Eagle Protection Act. Both of these laws make it illegal to disrupt or possess native birds or their parts. Falconers successfully petitioned the government to let them take wild raptors from the wild as long as falconers themselves regulate the participants. If the falconers are not being respectful of the birds it would be incredibly easy to strip their privileges.
In the same sense RC flying is a privilege from the FAA after too many people flew drones into airports and HAM is a privilege from the FCC to keep people from jacking up the airwaves.