The expansion packs such as Nuclear Winter, Caribbean Vacation and Duke It Out in D.C. were made by Sunstorm Interactive and another company. They were bought out by a few companies like GT Interactive then sold to Atari. With Atari going bankrupt, it's not likely we'll see them on the GOG shelves, unless they get their act into gear and buy the rights now before the company goes kaput.
the only one title 3D realms bought from sunstorm was DNMP and that was to have one more game to sell and port to x-box arcade to promote and fund DNF. Apogee never really cared about the cash in mission packs since they were more or less authorized fan mods in the vain of final doom. Shadow Warrior does include it's packs because they never went retail and sunstorms owner found the masters and mailed them to apogee to distribute as freeware he seems to not have the duke nukem 3d packs so atari must have them and is not willing to give gog the files to sell with another companies games. so unless 3DR or the new apogee buys the rights there never coming back out.