" There's no other reason to use it, except maybe paranoia or technical curiosity,"
How about idealism?
I mean 20 years ago, you would have been declared paranoid, if you said secret government agencies and big corporations track everything you do online - but now you just speak a inconvinient truth, most people are aware of, but try to ignore it as much as possible.
It is good, to have working alternative plattforms, in case there are really needed by us in the west.
But yeah, currently I do not use them either, because my last experience with them were "dark", too.
Because yes, the strongest incentive right now have those people not acting out of idealism, but because their content is not tolerated on the open web. Quite a shitty situation. How do one establish a "alternative, anonymous" communication service, without attracting all the kicked out elsewhere btards first?