The Roadblocks of AH
As I mused on this matter, it struck me that, in order to make AH more popular, certain problems/tendencies/ideas need to be dealt with. For your convinence, I have listed several of them below.
1. General lack of knowledge about real history
Throughout the last few decades, the amount of science the general person knows has increased. Today, any person on the street can tell you what DNA is, or what an electron is. An increase of general knowledge like this hasn't occurred in history. Without a greater background, a lot of subtler AH will simply shoot over people's heads.
2. Silly AH
Alternate history, like sci-fi and fantasy, does have an unfortunate tendency to become, on occasion, very silly very fast. A quick scan of the ASB section of the board can easily confirm this.
3. Determinism
The belief that history is controlled by great social-economic movements, in which individuals play only a small part, is not really compatible with alternate history, a living, breathing validation of the "Great Man" theory if there ever was one.
4. Politics
More so than science, history ties into politics quite tightly, so a historical discussion can easily get sidetracked into a political fight. This, of course, is proven by the various threads that have been transformed into Iraq flame-offs on this board. Also, revisionism can very easily slip into AH, leading to AH stories becoming Holocaust denial works and so such.
Just some thoughts on the matter.