I agree, many of the open source licenses are not pairwise-compatible. But the fact that GPL is a strong copyleft license makes collaboration more difficult.
And the idea that CDDL was made specifically to be incompatible with GPL is at best a speculation.
See Bryan Cantrill's video about the history of Solaris [0] and about different licenses [1]
[0] https://www.youtube.com/watch?v=-zRN7XLCRhc
[1] https://www.youtube.com/watch?v=Pm8P4oCIY3g
> But the fact that GPL is a strong copyleft license makes collaboration more difficult.
The problem is that both the GPL and the CDDL prevent further restrictions to the license. This actually has very little to do with the copyleft; plenty of other licenses (including the CDDL) prevent further restrictions on redistribution, even without imposing a copyleft.
