Yeah, it just was played up as if it had more significance (I think it was tied into Walt's comic book in Season 1), but apparently it had no real significance other than a minor detail.
The season 1 bear that Sawyer shot was just them laying the ground for weird stuff to go down, I think. Like "Hey, we need this island to be weird. You know what's a weird thing to see on a tropical island? Polar bears, motherfucker."
The next bear (iirc) is the one that attacks Walt after he storms off. The implication is that he called it to him after reading the comic book (Hurley's spanish comic book with the giant polar bear that Michael burns). This was more to demonstrate Walt's special-ness, I think, than to play up the bears, seeing as we also had the flashback where he was reading the book about birds and that same exact bird killed itself on his door. The bears were just convenient because it was already established that bears were on the island and they're also dangerous enough to create reasonable conflict which Michael and Locke could use to bond.
The next (and final?) bear in the series is the one that drags Eko off to its den. I genuinely don't know what the point of this was. A lot of the Eko stuff around this time doesn't make much sense and it feels like they were setting up all kinds of cool shit and then said "fuck it" and killed him. And the whole Locke sweat lodge Boone-y "clean up your mess" hallucination doesn't really cut it for me, seeing as it's Locke's fault that Eko nearly blew himself off to Arzt-land in the hatch but it isn't really Locke's fault that a marauding polar bear decided to drag him off (Also what was the deal with the toy truck in the bear's den? Did that ever get explained?).
The cages were there probably since the writers needed to explain how the polar bears got to the island and they'd already introduced the Dharma Initiative as this mysterious cabal of utopian science experimenters and the Others needed somewhere to lock Kate and Sawyer up so hey, maybe one of their stations was an animal testing facility and the Others have taken that over. Cool, we can do like a marine bio thing and lock Jack in the dolphin/shark room and he can accidentally flood everything and Ben can run away and leave Juliet to die and also speaking of Ben maybe his buddy that rabbit with the number is a Dharma rabbit.
Everything else is just references to their existence, like in Season 5 when Pierre Chang threatens to send Hurley to Hydra Island to shovel bear shit or when Danielle says "If we're lucky it's just one of the bears."
So yeah, I think the bears were more just a vessel for other elements of the show than they were an actual mystery in and of themselves. Like a way of saying "hey everyone, look how crazy and weird this island is!" or "look how special Walt is!"
Found this list. More interesting since it lists all the characters, and makes fun of some of them. (Not very detailed in terms of describing them, though... so kind of disappointing there.)
http://jezebel.com/every-single-person-on-lost-ranked-from-most-to-least-1546174780
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this is pretty funny. I appreciate the list-maker's appreciation of the Scott/Steve gag.
EDIT: I probably know way too much about this show. Like, is it sad that I can pull up pretty much every instance of polar bears off the top of my head?