Your point? If those lynchings had been orchestrated by people meeting up in person instead, nobody could know what people are talking about or help police track the source of the messages either.
In either case, to actually lynch someone, you still need to go there physically and actually do the deed. WhatsApp chats don't kill; dudes with weapons do.
The point is the scale. Law enforcement was scaled and equipped to meet the challenge of in-person lynch mob formation. In-person meetings are risky, finding like-minded people can be a challenge, etc.
Encrypted comms gives a huge asymmetric scale benefit to those who have these crimes committed. What it hasn't scaled is the ability of law enforcement to respond. And that's a choice, one which is open to criticism.
In either case, to actually lynch someone, you still need to go there physically and actually do the deed. WhatsApp chats don't kill; dudes with weapons do.