I think it's pretty well documented at this point that they were mostly making shit up as they went along. Now I don't think writing like that is inherently bad, but it can make it hard to stick the landing or come up with satisfying conclusions to your plotlines, and I think the show failed to do both, at least for many viewers.
Maybe I'm cynical, but I never really had the trust in the writers that some viewers had, I remember even on season 1, the moment they started introducing the numbers I was thinking to myself - ain't no way this is going to have a satisfying ending. Like, it can be a math thing or some obscure reference to some random shit, I remember looking at people speculating about that on the internet and thinking, man, ya'll going to be disappointed. Like, we don't think the writers really have the answer's to life's deep mysteries or anything, right?
And to be clear, I'm not sitting on any high horse here or saying that I'm like smarter than you all, in fact, such cynical approach to fiction is quite often counter-productive to your enjoyment, and it was certainly the case here, I mean, if you were able to suspend your disbelief and love the ever loving shit out of the show all the way through then you are the clearly the winner here.
I think I got that from watch the X-Files, that show made me realize that it's way easier to dangle mysteries than to resolve them in a meaningful and satisfying ways. Though I do think that the X-Files had less focus on the overarching mysteries than Lost (and it's also why my favorite X-Files movies are pretty much all standalone episodes).
Anyway, I think that's why I'm not that mad at the writers, but at the same time, this is also why I lost interest in the show sometime on Season 2.
