Comment by ryao

The OpenZFS code is based on the original OpenSolaris code, and the license used is the CDDL because that is what OpenSolaris used. Dual licensing that requires the current OpenSolaris copyright holder to agree. That is unlikely without writing a very big check. Further speculation is not a productive thing to do, but since I know a number of people assume that OpenSolaris copyright holder is the only one preventing this, let me preemptively say that it is not so simple. Different groups have different preferred licenses. Some groups cannot stand certain licenses. Other groups might detest the idea of dual licensing in general since it causes community fragmentation whenever contributors decide to publish changes only under 1 of the 2 licenses.

The CDDL was designed to ensure that if Sun Microsystems were acquired by a company hostile to OSS, people could still use Sun’s open source software. In particular, the CDDL has an explicit software patent grant. Some consider that to have been invaluable in preempting lawsuits from a certain company that would rather have ZFS be closed source software.