I suspect the answer to your question is just that the perception is there wouldn't be enough traffic to justify the forum. Sure, there are forums with very little traffic -- but I think in most cases the forums persist due to history.

You could always make the case for an Aloha section over in the Suggestions Forum.

In case you're interested...

There are 4 posts this year in the Other North/South America Frequent Flyer Programs forum:

FC on Aloha: like domestic FC or something better?
ALOHA AIRLINES: A Hot New Honolulu Fare
ALOHA Island pass - can you accrue 14,000 MP Miles?
US airline panel OKs Aloha loan requests

There are also posts over in the United board, such as:
Aloha Code Share
Using 5,000 UA Miles For Hawaiian Island Travel
A question about getting UA miles on Aloha flights
Aloha 1st class

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