In short, because higher interest rates weigh on the price of fixed-income securities (which are a main component of any bank's asset portfolio). The more important issue was that they rose incredibly rapidly, as the Federal Reserve sought to combat a wave of double-digit inflation ignited by soaring energy prices thanks to two OPEC-led oil embargos that decade. This is why Bank of America is so asset sensitive and will earn $5.3 billion more in additional net interest income once rates reach merely a percent higher than they were at the end of September.