I suspect the banks feel they have to do this purely out of due diligence. They can't be seen jumping into some new technology over which they have limited control, but if they try with something they have full control of then that is seen as safer. As you say, probably nobody will use these systems, but nevertheless the banks have to go through the motions. It's a learning and experimentation phase. Eventually they'll switch, of course, and use Bitcoin or Ethereum proper, or whatever emerges as the dominant and safest coin.