As to why it's not fitted, probably the most common argument against is it encourages pilots to take more risks.
Funny, I have a similar reaction to low time R44 owners wanting the autopilot that's now available. Some pilots will push on in worse weather hoping the autopilot will save them, which it probably WILL if they don't hit a wire or tower... It's hard to know for sure how aids like that will effect the total accident rates.
Similarly I could see the synthetic vision having that effect, except that in the case of Kauai it seems like people are already pushing pretty darn hard. My hat is off to the guys flying those tours every day. Additionally though, I think the tour pilots are probably very aware that if they actually punch in and have to use SV or instruments to get back to VFR, the people in the back aren't sworn to secrecy. If that's happening too often I imagine it would be visible to FAA etc.
I'm convinced my balls must be shrinking in size, because in years past I would push pretty hard on VFR weather, but in recent years I've noticed myself canceling flights more. A while back I mentioned to a fellow pilot that I have simply had enough of being scared in the air.