Why does everyone use the polar bear as a criticism of Lost?

I just finished the show, as in the tears are still running down my face as I’m writing this, but since starting the show all I’ve seen is stuff about ‘what about the polar bear?!?!?!’.

Am I wrong in thinking that this WAS explained in the show? We saw at multiple points that the Dharma Initiative were investigating things around the world (shown when Charlotte is in the desert and finds their logo in the sand). So is it too much of a jump to assume that they decided to bring over certain animals for testing purposes?

On a more title-related note, its confusing to me that people still use the polar bear, which was super unimportant to the show anyway, to form criticisms about the writing of the show overall.