Maybe people ban them because their bonus is absurdly good and they dominate SoA and Non-Round winning clans? Maybe its because they're the best mono-clan option in the game? Maybe its because they have bonus protecting abilities that make them extremely tricky to counter? Take your pick. Rescue is generally considered one of the most powerful clans in the game, especially in star limited formats like ELO, so it really isn't ridiculous that bans are thrown their way. One of the risks you have playing a top tier clan as a new player in ELO, (like Rescue, GHEIST, Piranas, or AS) is that you're going to experience a lot of bans.
Because its voted upon, played with and against a lot, their bonus forces you to pillz against every turn, two SOB cards to remove the relief you might of gotten against the bouns. To stop people from playing it so much, remove the stronger cards from the clan.