Sure they exist, does anybody actually use them? We're talking about the average user, not someone who is so in the scene they have multiple private tracker accounts.
Bittorrent, by definition at the protocol, includes sharing all pieces you have downloaded as soon as the piece is completed and finished its hash check[1]. The fact that there are nonstandard workarounds for this changes nothing for the broadly shared default that almost nobody is going to go out of their way to change, especially if it means using a specialized client.
It's just the same technicality as if you said "due to the way how video streaming works, downloading is inherently distributing". It just isn't. You can do it (videoconferencing has this as a default), but it's irrelevant.
