I find that more than the rules, more than the expense, its attitude and mindset that's having the biggest impact on the game as a whole (at least in the US)
This is not saying that it's not expensive, because it is
And it's not saying the rules aren't a mess at times, because they are
But I find the issue is attitude and Perception. Overall
40k is a -good- game, perfect? No but it is a good game none the less for what it is, and it really is the only one of its kind. In that go through Infinity, Warmahordes, whatever game you wanna insert there is no other quite like
40k.
Tournament play is not everyone's cup o' tea, yet local game stores and groups adopt that mentality all the time using ITC and other big tournament rule sets as law which there are a lot of people who don't like this (I'm one of em, I just pulled myself out of a big local
GT that I was looking forward to because of their adoption of ITC regulations.)
Locally, for a while several years ago,
40k night became tournament night or Tournament practice night and if you weren't doing one of those things you had two options, hang out and talk and watch or face tournament list after tournament list. And this eventually killed off a swathe of the community because more and more people got bored/tired of this and for almost a year
40k was dead.
Now it's back, and we have a strong group of 10-15 players and a few who are completely new to the game and the tournament focus has been shifted to a league style play and it's done wonders as the league Games are power matched by the league head.
Does this mean tournament play is bad? No not at all, we still have a strong tournament scene. What it does show is that the "tournament mindset" is contagious and can turn into an infection in places that it doesn't belong. Much more so than casual play infecting the tournament mindset.
There are places for both and both styles should be venerated equally, as they have equal Merritt in the gaming community at large and neither is less valid than the other but forcing any mindset over 100% of the local meta can be cancerous to the community.
The other type of mindset that can lead to the fall of a gaming community is the attitude of outside individuals. Now this can be former
40K players, people who don't understand wargaming or don't "get it", and those who don't play the game in question but instead form opinions and press them on the people who do.
A big example of this that I have experienced here locally are a bunch of X-Wing players that are former board game players and this is their first foray into tabletop gaming Beyond a board game. They've taken up the attitude that
40K is stupid and that nobody should really play it but should instead play X-Wing their game of choice and do get very vocal about this point make stupid jokes and laugh at the people who are playing
40K on tables across from theirs. This has led to new people not coming back to our particular store because of this attitude.
You're also experiences heavily from former
40K players that left
40K for a different game for any one of a number of reasons. However they have been taken it upon them as their own personal responsibility to be rate put down and otherwise talk poorly about the game they used to play and what turns out to be a very sad irritating and mostly an effective attempt at getting people to join them in their game of choice. The local Warmachine groups being the biggest perpetrators of this Behavior.
All of what I have said and listed above have been the major factors in the reduction in size or the entire elimination of the
40K Gaming Community in several cities across the United States that I visit. And as such leads to more proof from my opinion that it is truly the mindset of players and local gaming communities that have the biggest negative impact on the game.
I will also note that in my travels across the pond to the
UK and various other European countries where I find
40K and tabletop gaming General, the attitude is much much different. While tournaments, Games Workshop hate, and tabletop gaming competition between different games certainly still exists, it does not contain near as much toxicity and Vitriol that the communities in the United States seem to experience. (Aside from Warmahordes players vs
GW players I think this is a universal eternal hate.

)
So once again when you look around at your gaming Community wherever you might be and you have the feeling that it is falling apart, take a look around at the causes for it and I guarantee you'll find a good portion of it is from Community attitude and mindset as opposed to the actual game itself being a failure.