Because what your culture had been put through was simply, too painful to recall, because you were so mistreated, abused, by some OTHER culture, that, as a group, you’d, blocked out that part of your collective pasts?
The loss of memory, by an entire culture, how, could you, as a culture have, forgotten about the SHITS that happened to your ethnic group in a certain time in history? Don’t you think, that by recalling up that part of your collective pasts will help you, find closure sooner? Or, would you, rather, keep on, living BLIND?
The loss of memory, by an entire culture, this may be WEIRD and WHACKED out, by those of you, who don’t share that collective bad and painful part of your pasts, but, it’s considered, “normal” for those who’d been prosecuted, some point in time.
Life, the Obstacle Course 