I have no way of knowing whether the other factions just stumbled on the Cosmic Icosahedron (henceforth referred to as CI) or if they had intelligence. Space is big, and random chance is seldom as random as we think. Even so, all they needed was a rumour, and they would likely have gone searching, and just as we were able to detect the radiation signature of the CI, so would they. If I were a pirate, I’d be right out there too, looking for the fabled treasure.
The question about whether the CI has only just been found or whether somebody was already in possession of it, and it was recently stolen, is interesting, though I have no data to answer it at present. I would postulate that if somebody had found it long ago, they would have done something with it, and whether that means advance their civilization by means of its tech, or destroy it by careless meddling, we would probably be aware of the results. Either way, the CI would not be left unprotected in the middle of a nebula, I think.
How the CI could have stayed hidden so long is another interesting question. I don’t know precisely where Lancer’s crew found it, but since they were scouting covertly I assume there were other ships in the vicinity. Again, I don’t like to leave the answer to random chance. Perhaps the CI had some cloaking field that kept it hidden all this time, and it only recently failed, due to its age. Perhaps there was some peculiarity in that sector of space that interfered with sensors, and that recently changed – it ought to be possible to determine if that’s the case. It’s something our scientists and engineers would love to investigate, I’m sure.