Not the only reason. Those tools are more developed and can do a lot of things that can't be done here, and it can be faster. Discord is chat, full on media sharing, and voice chat if desired all rolled up in one.
Yet, I do have a problem with it not being on the blockchain if it is discussing important things about steem/it, but even steemit inc., keeps things off of the blockchain until they are ready.
As far as these people... Bernie hangs out on steemit.chat in the #price channel and goes by the handle nextgencrypto.
You can jump on steemit.chat and scroll back and grab huge amounts of data and "personality" from reading the discussions there. Then you can screen grab them, or otherwise grab them and post your findings on the blockchain. :)