@cassidyclown I think it's the lack of a safety net.
I suspect people can feel that there is no bottom underneath them when they are on the fediverse. The sensation of your feet dangling off the ledge is uncomfortable for people who have never been anywhere they could even see it.
People have been socialized into being uncomfortable with what the fediverse will always be, and good fucking luck breaking that conditioning.
I personally don't think there are any great reasons not to, that a lot of the meme rebuttals about oh what server oh feed is empty are made by people you would never convince anyway.
But then again, I'm here, and they're not, so of course I don't see any strong objections as legitimate. You probably have to mature into being able to want the fediverse, so to speak, to develop an appetite for it. Few do, especially among those raised on contemporary, large social networks their entire online lives. I think that's why the fedi userbase tends to skew towards traditional definitions of nerd and geek, or pre-dotcom-bubble in their introduction to the web. As part of user retention, corporate social networks probably take somewhat active discourage venturing beyond, even to competitors to an extent that most users would only come here out of desperation or necessity.