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 also notice that but do they need that they already have a channel of their own inside their platform, and if they want an update they will just send newsletter to their members, Discord is good it was created for gamers and since some gambling have sports betting in their platform they prefer using Discord then Telegram.