https://wccftech.com/blizzard-world-of-warcraft-legacy-content/

Supporting older World of Warcraft legacy content in new patches and expansions is difficult according to Blizzard’s technical director on WoW, Patrick Dawson.

Since its original release 14 years ago, World of Warcraft has received numerous patches and seven expansions, adding new content and features to the existing game. While most changes affect end-game content, new additions might also influence older content that was already there, and according to Blizzard, considering all these factors is rather hard.