The problem with that argument is that the Treasury yield curve isn't currently inverted, and that actually matters in things like this, unless this bank is in a different country. Fixed rates are also typically higher than variable rates at any given point in time because they carry greater interest-rate risk, so that would tend to make this situation more unusual.

Most likely, the bank sees value from customer acquisition in the savings account case, which could be more effective at up-selling/cross-selling. If you want to see this in action, look at the marketing pages at Capital 360 for savings account vs. CD. Capital 360 has a .75% savings rate and a .40% 1-year CD rate. With the savings rate they can connect with checking (overdraft and other fee possibilities) and set up direct deposit (customer retention, low acquisition cost asset growth). The savings account isn't actually completely fee-free, by the way, they charge $40 for wire transfers, but you have to find the fine print.