I haven't seen any Gamblig Platform who used Telegram for Promotions, most I know is that they use Discord.
Do you have any Idea why they don't have any Telegram Communities? and why does it seem they don't use this platform for their promotions?
I think there is also its just happen that most telegram promotions are done by Bot and people in telegram are used to that so they are not interested.
and also sad to say that majority of Telegram users are Bounty hunters and not typical gamblers so the target audience is not that achievable so this maybe the reasson why they are not focusing in TG platform.
But of course there are some groups that i joined who has this features of campaigning .
Discord is a better platform for promotion since it is more convenient and it offers more feature than Telegram. There are also a lot of spammers and bots in Telegram which can easily swarm a group. Discord is user friendly and organized since they also have a bot to assist you with commands.
Same as what i think why the reason people not to tend advertising in TG,because of Bot and spammers.