My guess is the reason for kidnapping was so that France (and its NATO friends) are added to the CC moving forward.
Discussion
I'm fully aware Telegram group chats are not e2e encrypted and their off-by-default DM encryption is dodgy.
But there's still SSL and even if the French government had a backdoor for that, it's a lot of work to monitor the Russian internet that way. It's easier when Telegram forwards the chats to them.