There are 20 movies that came after the Lion King and before Frozen and another three after Frozen that Walt Disney Animation Studios created. Outside of Tangled and maybe Mulan none of them were as heavily marketed as TLM, BATB,Aladdin & Lion King continue to be. Heck, Mulan is not even a princess.
One other one I forgot that really should be added to the marketing love affair is Stitch, sort of the equivalent to Pooh in a sense, which also randomly came out in the middle of the lull.
Even if marketing doesn't love them, the 19 years between Lion King and Frozen certainly had some worthy content. Hercules, Mulan, PaTF and Tarzan were certainly all at least 'good'. I'm somewhat partial to Emperor's New Groove, but that's a very ignored movie.
Reviews seem to match marketing pretty closely, except for Emperor's New Groove: https://www.rottentomatoes.com/guides/best_disney_animated_movies/#