There is no random hassle that get your account/group/channel deleted(unless you are doing real CP, which is a giant red line of telegram) or random limit for size of the group. And easy to use. That's it.

Also the apis are almost completely free, so you can do lots of creative projects for fun.

Most people dont give a shit about security. Telegram is easier to use than signal and has more features because auto encryption makes stuff like public chats difficult.

Exploit their smartphone then email tidbits of their more outstanding Facebook chats, SMS messages, maybe some nudes, and recordings of their phone calls. You will see the "I don't care about security attitude" do a hard 180 real quick.

Sure, but for now they dont care.