My other thought was that maybe the island escapees were trying to keep a low profile and didn't attend the funeral as to not attract attention to themselves. That's the vibe I got when Jack asks Kate if she went and she says "why would I?" That could also be a reason why they met in such an isolated location. Maybe Jack is famous for being the "hero" and getting people off the island, but perhaps people like Kate and whoever else got off the island do not want to make themselves known. (Kate especially I guess, since she, you know, killed someone).