It seems as though Naomi had wanted to retire or sit out a season due to burnout. Due to letter writing, she & Peter started training again, but then they withdrew from Nationals due to her cyst. Then she became pregnant. So, it's not quite the same as L&T wanting to come back just for Oly's.
Some of the other's are a bit different. I have a feeling that their federations may have asked them to come out of retirement since they don't have any likely medal contenders. FP&M fall into this category. I'm not sure what Silvia's thinking since she was never at the top, but at least she's not going for the only spot on the team.