When it comes to issues. I see only one reason for legacy wow not to be released. There is a major risk that modern retail wow will lose much of its player base if legacy servers are released.

Here is the problem with that. In modern wow blizzard can continue to add infinite content, keeping people in the game and paying their monthly bill. If legacy servers are implemented. It would be almost impossible for blizzard to add content to multiple games at a rate that would keep their playerbase. Not to mention adding content to legacy servers would kinda invalidate the point of having legacy servers. I've been in this scene for 6 years, wow is great but it gets boring when no content is being released. Get the most die hard player to play long enough and he will run out of things to do.

Legacy wow if released adds an unnessisary competitor to retail and complicates the upkeep and costs of wow tremendously. The game has been in decline for a long time, and legacy servers could be the cause of its eventual death. Blizzard will by no means release official legacy servers, because it means the beginning of the end for their aging masterpiece.