A couple of things:
- back when I started moving groups WhatsApp wasn't E2E-encrypted
- one of those (Zuck and Durov) is a known bad guy and it isn't Durov. The other might or might not be a bad guy, but if he is he is truly hiding it well for now.
- also once I have managed to get people to understand that multiple messengers exist I hope much of the work is done already and the first groups have already been on Telegram so long that I might start to push them towards Matrix without triggering any bad feelings. (Yep, possible: the oldest one I've seen jumping from WhatsApp to Telegram with no issues at all must have been well over 80.)