Can create private groups in Briar and others you listed.

Most don't care about privacy and censorship resistance even today, including criminals. That's why they were using rubbish, such as telegram. 

Like locust, they shall go everywhere there's something "free as in beer" and least effort.

Seems irrelevant where locust go, as long as it's not your field, unless monetising them somehow.

Here in Asia, majority use other mass surveillance rubbish - WeChat, Line, Viber, Whatapp, Zallo - wherever their gangsterment runs the herd.🐑🐑🐑
They've never even heard of  the ones we use, and would not switch now.

Only ignorant and lazy people used telegram as their main messenger. "Play stupid games; win stupid prizes!"🙃