> It is probably more accurate to claim the GPL was designed to be incompatible with an entire class of licenses that includes the CDDL, and the MPL on which it was based and any future licenses similar to or based on licenses in that class (of which the CDDL was given that it was made after the GPL).
Given that work was done to make GPLv3 more compatible with other open source licenses and that GPLv2 predates both of the licenses you mention by quite a bit I'm inclined to think that's nonsense.
If being compatible with anything were the goal, the FSF would have opted for the CC0 license. Since the GPL is not compatible with things on that level, it is designed to be incompatible with certain things. Some subset of possible open source licenses definitely were excluded as part of that.
Given that work was done to make GPLv3 more compatible with other open source licenses and that GPLv2 predates both of the licenses you mention by quite a bit I'm inclined to think that's nonsense.