Since the average player spends far more time thinking about playing than they actually do play, they spend that time doing what they can. It's hard to put tactics into practice without an opponent, so they work on what they can: creating and tweaking their army lists. The purpose of optimizing your army list is to make it so the army can almost play itself--such that if you make many mistakes during the game, the raw power of your army can save you from defeat. The tactical element of the game still exists, but takes second place to the army list.
Now I'll go off on a small tangent (or an analogy, you decide)
In the past three years I've gotten into the sport of paintball. In doing so I've browsed the various paintball forums, etc., and see much of the same stuff, as it applies to paintball. The most common newbie question is, "how can I make my paintball marker more accurate?" There are endless discussions about how to upgrade your marker to make it more accurate, shoot farther, and shoot faster. There's also a good amount discussion about camouflage (related to woodsball games), and which is better.
But there is essentially no discussion about tactics. It's all about equipment. At a recent game I attended, the paintball place was, as usual, filled with guys in head-to-foot camouflage (like me), and $1,000 electronic trigger 20 bps (balls per second) tournament guns (not like me) running around.
Me in my multicam and my Alpha BlackOne of the off-duty referees (who are all very experienced players) decided to play a game. He overheard me griping to a friend about players with 20bps electronic guns and how I don't like them because in my opinion they are against the spirit of woodsball. He held up his Tippmann 98 custom paintball marker (an entry level, inexpensive paintball marker), and commented "This is all you need." (As an aside, he was dressed in a white t-shirt and basketball shorts--no camos for him) With that inexpensive, entry-level gun, t-shirt and shorts, he proceeded to annihilate hordes of opponents with equipment that must have set them back over a thousand dollars (or more likely, set their parents back). It was awesome to see.
Anyway, the point is that if you're a good enough player, it's your abilities as a player that earns you wins, not the abilities of your equipment (or army, if we're talking 40k again). A rationalization about building "competitive" army lists is that it's the only way to level the playing field. The only way to ensure that the game is "fair" is the unspoken agreement that each player was field the most "unfair" list they can.
Well, screw that. I don't make competitive lists, and I never plan to. As a player I'm not in it for the competition, and I see the game more as a simulation (albeit a fantasy one) than a competition. From that perspective, I'm in it more for the generalship than the logistics. In the real world, generals essentially never get to choose their forces. They have to make do with what they have. And what they have is usually far from ideal. It's the good general who can adapt to a fluid situation, making most of the assets at his command.
Fortunately I play with like-minded players. We all want to win, and we try to. But we play fluffy armies, and the result is a more relaxed atmosphere, and a fun game.