One reason is that OpenPGP is already widespread and you may use known OpenPGP key to establish shared secret and switch to OTR then.<p>Another reason is that OTR is not multi-party. mpOTR [1] was suggested by OTR authors (Ian Goldberg et al.), but I am not sure you can find at least one peer who has it installed, and it is not maintained. So for XMPP conferences you may still want to go with OpenPGP.<p>[1] <a href="https:&#x2F;&#x2F;dx.doi.org&#x2F;10.1145%2F1653662.1653705" rel="nofollow">https:&#x2F;&#x2F;dx.doi.org&#x2F;10.1145%2F1653662.1653705</a>