the horde are made up of very different factions that allied for mutual survival and convenience originally - the orcs, tauren and trolls that formed the core of the horde in wc3 have cultures that mesh well together and can coexist.
then, they added the forsaken, who are, at least culturally, based essentially on shared suffering, the perception of personal and social loss, and bitterness.
then, they added the blood elves, who were motivated largely by desperation, both for allies and new sources of magic.
this situation, especially the inclusion of a faction of essentially evil undead into an alliance of otherwise forthright, honorable warrior cultures, was never really tenable, and will continue to cause the horde problems for many years to come.
also, lor'themar does like nothing ever so he's kind of a non-factor, especially because the blood elves have the magic they need and are basically in a narrative holding pattern, like the draenei are/will be for a while.