Because the price of resistance is likely to involve them doing their damnedest to figure out your relatives, and then holding them hostage. And or making you wish they'd kill you once they catch you. And/or making it clear that your resistance results in much more suffering.
All the things that happened in Vichy France... but with the tech to back it up and really root out the 5th column. And the ability to use the Dr. Mengele type as a visible tool. And the forensics to get it right. And, undoubtedly, there are collaborators who will make certain the databases get turned over.
Simply put - while a small percentage of the population will resist such, it's quite possible, with proper investment, to make it odious enough for the majority to sell out resistance fighters. Especially if the occupation forces are not generally brutal, learn the local language, and the resistance fighters are given the chance to surrender before familial punishment is inflicted. Especially if resistance fighters are "reconditioned" then released.
We know from canon that there is, by TL15, tech that can suppress or subvert one's personality. (Expedition to Zhodane.) Given that, a few resistance types implanted with sleeper orders, ratting out a few others, who likewise get them... very quickly, one can, in theory, stepford the majority of the resistance.