I know these peoples use multiple accounts to farm airdrops. I am not active in airdrops, but I am in two discussion group where people share their thoughts about the current airdrops and upcoming airdrops. It is possible they are spammers which could lead their account get frozen or locked to send messages to people. But that should not be enough to get someone's account banned. Nobody knows why their account was banned since telegram never inform them. Some of them says it could be because they promoted some bot through their bio. Or it could be because they use multiple account on same device. Or probably because they use alternative apps like telegraph. So, accept the fact that you know nothing about the the recent telegram account bans.