There are bigger considerations here for these banks than the gains they would make from the failure of small banks. They know that they are in a very nice position with the government guaranteeing all of their debt while at the same time leaving them free to make as much profit as they can. They know that the mass failure of regional banks while big banks gain would be a political event as much as a financial one. They know that they are some of the most widely hated organizations in the US, and that the political fallout from such an event would not go in their favor like last time, so they will pull out all the stops to prevent it from happening.