BoA and other banks did not ban Bitcoin. They have no regulatory oversight to ban. They did, however, stop allowing people to buy cryptocurrencies on credit (meaning loans and credit card purchases).

Also, checking out the articles you linked, the closest thing to "banning" is that they no longer allow their on-staff financial advisors to buy Bitcoin on behalf of their clients: "the company banned financial advisors from buying bitcoin-related investments for their clients."

At the end of the day, it's not in a bank's interest for their money to be leveraged to buy crypto-currencies, so of course, they're going to limit that as much as they can within their customer's accounts and terms of agreements, but the banks cannot ban consumers from buying with our own money. Only the government can regulate that!