Simply because it would make the situation much more flexible. The current rate has been in place for many years. The economic context has changed, and it took 30 years before we decided to ask the question again.
Similarly, in the Consumer Protection Act, new rules were introduced in 2018 that provide for high-cost loans. Again, this high rate is calculated based on the key rate. That allows for some flexibility and helps avoid having to go through a legislative process again to change the rules along the way.