Because no one's actually going to Mastodon. It's really that simple.
If you wanna delve into the details of why people so often avoid the platforms that FOSS enthusiasts tend to recommend, that's an interesting question, but we gotta be clear here, we already knows who's successful and who's not.
People one go where the technologically literate tell them go. If it wasn't for me, my family and friends wouldn't have gone on iOS, WhatsApp, Signal, you name it. If we give the thumbs up they know it's not bad if they migrate. Of course they can still decide against something if they don't see the value, but we can have significant impact on what platforms they use or not.
> People one go where the technologically literate tell them go.
No they don't. If this was true, my wife's family would be on Telegram or Discord, haha. We actually did go into Telegram briefly, but they all dropped out. What got them to switch from SMS to WhatsApp was her parents temporarily moving to Austria.
What videocall service other than Discord lets a normal user individually adjust other call participants' relative volume or even mute them? Because for me, that's the killer feature.
If you wanna delve into the details of why people so often avoid the platforms that FOSS enthusiasts tend to recommend, that's an interesting question, but we gotta be clear here, we already knows who's successful and who's not.