I've ranted about this before (here and here). So, I'll be brief. Sort of. But, as long as writers in my realm of influence insist that something couldn't or wouldn't happen in somebody else's story universe, I'll keep making this point: it can happen if the writer says it can happen.
I stopped watching Lost after Season One so I wasn't invested in the finale. But one comment I saw about the wrap-up said that the island could not possibly have been purgatory since people do not meet and fall in love in purgatory.
Interesting. But, not so.
Maybe in purgatory, as you see it, people do not meet and fall in love. But this isn't your purgatory or my purgatory or God's purgatory. If it's purgatory at all, then it's Lost's purgatory. Your opinion doesn't count. Nor, does mine. It is what the writers declare it to be.
Writers are the gods of their own universes and if, for example, a story reality establishes that all birds are flightless, then they are. If writers decide to leave the question open to interpretation, then birds may be flightless and they may not be, depending on individual perspective. The Lost finale may be open to interpretation. I really don't know.
What I do know, however, is that finales disappoint. They must. There's no way to please everyone. But there's a difference between failing to suspend disbelief enough to make something work and something not working because it's not possible.
We're writers. All things are possible.