EDIT: This got really frikin long.
It's quite hard really. Not a very easy question to answer.
From my point of view, there a few things that sparked this decline. After MoneyMaker you have the poker boom, everyone wants to play poker, because some unknown dude just earned more in one tournament than most people did in one or more years!!
Now poker is seen as an easy way to make easy money. You have people from all around the world turning to tables because international media made this look like it's easy to be a millionaire. These people are so convinced that they are the best (as we all were at some point) that they don't want to have limits set on the bet sizing, and no limit tables start appearing everywhere.
However, things like this don't last very long. Eventually people start studying the game, strategies start coming out. The game itself responds to every strategy and demands for a new strategy, a new way of thinking. It stops being that easy. Now the game starts requiring study.
What happens to those who don't study? Well, nothing, at first. Maybe they keep winning, maybe they keep losing... For a while. But eventually, especially over all these years after Chris, things balance out. People start losing money, and losing it consistently. Recreational players who were there to "have a good time" are now losing to regulars that know what they are doing. People who saw poker as a cheaper
blackjack and would just call bets to see if they got lucky are being smashed by aggressive players that punish them.
People start losing money that should be easy to win.
The easiest solution is to give up, and, one by one, they start doing that. It just keeps getting worse as times roll by. For every recreational player that joins the game today, at least two leave because they got tired of losing.
What do we do to turn this around? In my opinion, another spark. We need to restart the process. We need to repeat the same Big Bang that happened last time. We need international media coverage that shows poker as this easy way to have easy money again.
I don't know about other countries, but in
portugal you don't see any
poker news on national channels. We have RTP, SIC, and TVI, the 3 major TV channels that are seen by anyone in the country or travelling abroad that wishes to tune in for national events. From all these, only SIC covers poker on the news, and it's always the same story:
"
Today we talk about Susan. Susan was a very bright and innocent lady, without a trace of imperfection. Then she found poker. She now became broke, totally useless to society, is a drug addict, and went to jail. Good job Susan. Everyone is proud of you."
Ironically this channel is the same one that covers poker tournaments... At 2 am.
Portugal and Europe in general took another big step (that everyone was scared of at first) that demands that any
online poker room gets licensed and pays taxes. It takes some of that "Poker players don't contribute to society. Poker is not a job. etc" edge off.
Some coverage on why poker is a game of skill and not luck would be fine too.
Eventually though, poker will never die. What will happen is that people will just switch games. A few years from now everyone will be playing Omaha, simply because they aren't that many strategy on Omaha yet, or people don't know about them. Or most likely someone will come up with what at first will look like a ridiculous variation of Hold'em nobody even knows how to play, but if it gets big enough, the word starts to spread "Look, we found this new game. It's exciting, easy money, and nobody can break or study it yet".
And the cycle repeats.