Eloisa, I think any reasonable person can take a guess at why certain government actions don't appear to serve the best-interests of the general public.  When a politician relies on special interest money to get elected, his/her livelihood becomes dependent on serving those special interests (that may conflict with the public's interests).  

When it came to medical marijuana, I'm sure our lawmakers were trying to juggle very conservative anti-marijuana interests, big commercial interests (marijuana for profit), and patient access to medical marijuana.  In the end, it looks like patient access to medical marijuana got the short end of the proverbial stick. 

For a blue state, Hawai'i voters can trend toward the conservative side.  Like the OP indicated, there's a negative stigma surrounding marijuana and that means voter pressure on politicians.  Are we known for politicians that take a firm stand on issues?  Or are we more known for politicians that play it safe to get re-elected?