With trackers, you're revealing the fact-of-transmission, transmission-size, & endpoints to any number of unknown remote parties. Potentially, attackers not even on the privileged network-path from origin to destination could tee off a copy of your encrypted data for offline analysis.
With Magic Wormhole's rendezvous-server, only one server, run by the same person whose code you're trusting (& can audit), briefly relays encrypted control-messages. (It might even be limited in its ability to deduce the size of the transfer – I'm not sure.) And if that's still too much, you can run your own rendezvous server.
It seems to me the amount of information leaked in the BT Tracker approach is strictly (& perhaps massively) more, to more entities, than that leaked in using the Wormhole author's server.
Of course the nice thing about Magic Wormhole is that its security does not depend on server components to be trustworthy. Use the default servers, use your own, use a different third party server, it doesn't matter, your data is still secure.
Edit: If you are worried about privacy magic-wormhole supports transit over tor.