Both shows seemed pretty rushed. If I recall correctly, there wasn't a lot of time between the initial announcements and first stage appearance for both of these shows. Compare that to NEWSIES, which was initially announced 3+ years prior to its first appearance on stage. Granted, it was initially intended to be developed for licensing purposes only, but the statement still stands.
Like many folks have already said, the main trouble with TLM was the lackluster technical aspects. The division between land and ocean characters is a huge challenge that designers still seem to have trouble with. Every new production that has popped up around the world features something "new" in regards to swimming or the ocean characters. ("swim" wigs, flying as swimming, etc.)
To me, at least, TARZAN wasn't the best choice for theatrical development. The music in the film is wonderful, but is mostly used as background music for scenes, rather than a storytelling device. Also, TARZAN's stage design seemed more like a Cirque du Soleil performance than a Broadway "blockbuster." I actually think it would've been a better idea for Disney to collaborate with the Cirque creative dept. for a stage version of this as a show in Animal Kingdom or a potential replacement for LA NOUBA in Downtown Disney.
It's a shame that they pass over some wonderful films (TANGLED and even ENCHANTED) that could be adapted for the stage more easily in favor of properties that require extensive (and unsuccessful) risk-taking. Perhaps they could use some Imagineering magic in the Theatricals office... :)
Every living soul has got a voice - you've got to give it room and let it sing.