If you get your hands on the Kimba series box set, there's an interview on it with an anime historian (who presents himself as a fairly impartial judge). His conclusion? Inspiration and/or tribute. In fact, so he says, Disney's B&tB has many many tributes to a French film adaptation of the same fairy tale, and no one cried bloody murder then.

I would also suggest taking much of the "evidence" found on the internet with a grain of salt, especially since it seems by and large to be the rabid Kimba fans who are dead-set on proclaiming TLK to be a rip-off who go about constructing sites, if not entirely dedicated to the controversy, then with a rant associated with it. That and I've noticed on more than one occasion that they don't get their TLK facts straight (the pride does not live in the jungle, contrary to some of the claims I've seen) or have a penchant for keying in on broadly generic concepts (OMG, Kimba and Simba both have dark ear markings...never mind that lions really do have dark ear markings). They also seem to neglect the idea of archetypes (the quest, for example) when casting their comparisons.

Anyway, per why there was never a lawsuit: Tezuka's estate decided against it. The similarities were determined to be a series of coincidences and nothing more. Thus, as far as the respective legal teams are concerned, this is a nonissue long since resolved.

Which just begs why it has such a long life on the internet. Well, the whole thing smacks of corporate cover-up, or downright conspiracy, made even more juicy by the fact that, for almost a decade, this supposed "copy" was the highest grossing animated film to date. But, anyway, at the end of the day, my guess is, there were a few intentional tributes -- a la the aforementioned "To be or not to be" scene in TLK -- but the crew couldn't acknowledge them due to the legal team stepping in and proclaiming, sweepingly and erroneously, that no one on TLK's production staff had ever so much as heard of Kimba, let alone come into contact with any related material. And that gave this whole thing lasting infamy. Let's hear it for the suits.