The 1000Base-T standard came out around 1997 I believe, and they would have been working on that for several years prior. It would make sense then for the cabling standards at the time to look forward towards adoption of the new technology which would require 4pr cable, even if the technology of the moment did not need more than 2pr.

Buildings that were properly wired 10 years ago using Cat5e will support Gigabit and POE+ without any need to retrofit the cabling. That's the beauty of following standards. I think we need standards to have the longest life-span possible, and that means building the capacity to use technologies that we don't have on the market today.