Here s a weird theory maybe the motives for the time travel was maybe something happened to kairi like she gets killed brutally by something and to make sure that event never happens again. and maybe going by the time travel and from what stiensgate s time travel system no matter what events change the world line will link together somehow at the very end, meaning maybe the idea is that sora wanted xeanort to reset the world for balance to a different world line with balance so kairi would survive