IIRC the bans weren't successful because the Telegram client had a system which announced new servers/IPs via push notifications. So they easily evaded it. Plus, the agency responsible for the bans got a bad rep after accidentally banning lots of unrelated services, ruining random businesses in Russia.

Maybe they also understood that if you can't defeat them, lead them. Currently, Telegram has a lot of pro-war, pro-Kremlin channels.