I think you might need to look more at the symptoms. Have you noticed the fact that when asked, most people here will say something along the lines of, "I'm a card guy, but if I don't have my cards I'll do some coin tricks or mentalism."
The majority of this forum regards coins as a throw-away, a cheap stand-in for their cards. Hell, most of them would be utterly mystified to learn that T. Nelson Downs based his entire Vaudeville act on nothing but coins.
Not that I don't support this thread, but we all also need to address the cause as well as the symptom.
If we start off in a shallow manner, and try to break it down bit by bit, one of the major factors might be that coin magic is extremely hard compared to card magic (this is by no means ment for puning, there are loads of awesome card tricks out there but i'm being relative to the grade of effectivity). In coin magic you are usually constantly vulnerable to angles, and your body language plays a major role, within card magic you have a deck of card and you're usually not prone to angles. When you start getting into palming and such but now I'm talking about easier stuff. Let's look at an ACR routine, that effect is just stunning, and if I remember right is the only effect that actually fooled Harry Houdini. No matter who you perform it to, if the presentation is right it will blow away any layman.
Let's look at a Coins Across routine, non specifically just overall. A coins across is quite amazing, especially if presented correctly. But a Coins Across routine takes alot more body language and synchronising and misdirection than an ACR routine, and yet I still doubt it would be as effective (maybe now I'm being unfair seeing as ACR is one of the strongest effects imo).
Coin magic back in the days probably had more value to it due to that back in the days, you actually used money as a strong currency. Today that is taken over by bills. As we know one of the 3 major factors in life is money. Imagine to be able to just bring out money blantly from the air, real high valued money. To the spectators that just implies that "this guy could get so rich", and it would be more meaningful since they can relate. Today if you pluck a half dollar from the air, that is cool, but it will hardly solve your economic burdens. These are some factors I believe might be reasons. I'm sure there's much more to it and I'm also quite sure alot of you will disagree with what I have had to say.
Still, if we could see some contributions, good or bad, that would be awesome. Everyone starts somewhere.