Re Telegram - two main issues are apparently at play. One is child porn, the other is concerns about ransomware/extortion groups. The big concern is rightly about the first one.
With the later, groups targeting France (and the UK) have been dumping victim data on Telegram groups, with Telegram directly hosting the data and then failing to remove it.
Telegram is not an encrypted platform - the groups are plain text.
Telegram has <50 staff and 1 billion monthly active users.