In hindsight, an explicit "GPL compatibility clause" like the EUPL has would clearly been a wiser choice, but that wasn't clear in 2005, and it's too late for that now, unfortunately.
On the other hand, you could also blame the GPL for not recognizing that other copyleft licenses exist; they also could have written a compatibility clause in GPL 3. "CDDL is incompatible with the GPL" could also be phrased as "GPL is incompatible with the CDDL".
Yes, I agree; there's a few other topics like this. I call this "hacker conspiracy theories", because at this point that's basically what they are.
I mostly comment on these things for the benefit of innocent onlookers, who were not yet around when all of this went down, and not to convince the person who posted it.