As title above, why are opening books so popular? I am sure that most players know that middlegame and endgame books are ultimately much more important for improving one's chess strength. That is not to say that openings are not important, but it seems to me that a good 80% or so of chess literature are opening / repertoire books, and that means that these are the most bought ones.
I think there are number of reasons why these are so popular:
- It is easy to start learning openings. You can read about ideas and memorize some lines. It is not so easy to learn middle game or end game in similar fashion.
- A lot of players want to get an edge from the start- hence the focus on openings.
- People enjoy reading them
- They are easier to write than good middle game books (as indicated by different chess authors)
It is questionable if middlegame or endgame books are more important. There is an argument to be made that you need something other than books to learn good middlegame / endgame skills. Openings on the other hand can be easily learned from books.
Because not everyone who is "interested" in chess is trying to optimize their chances of getting better.
A number of people treat chess games as if they were "stories." They start reading a game/story, get bored, and either move on to another one, or two a past time altogether. They're interested in how things start, less interested in the middle or the end of it. That is, they lose interest when things get beyond a certain point.
Opening books offer a much bigger return of investment than middle- or endgame books to a much bigger target group.
Middle- and endgame books are better for the relatively small group of people with a lot of time and ambition. They want to seriously invest time to seriously improve at the game (and potentially reach a 2000+ rating). For this goal, one needs to cover every important aspect of the game and "dive deep", even if it's a chore sometimes.
People with no or not much ambition will most likely never touch any chess book at all. They are probably the biggest group, but irrelevant to the publishers.
However, people who don't have the time, but still some ambition will find that a good(!) opening book will serve them well enough (if it is focused on middlegame plans instead of memorizing lines). They may not learn all possible middlegame patterns (arising from any possible opening), but they will learn the typical middlegame patterns of their opening of choice, and that will probably cover about 70-80% of the games they play. They won't be as easily able to switch opening lines as part of preparation against some opponent, but as long as they get to play "their" opening, they will feel comfortable enough. Likewise, they will lose some endgames because they lack the theoretical knowledge, but again, this will most likely only affect a small percentage of their games.
An important point here is that if they do invest a small amount of time to go to their local chess club's training sessions, opening books get even more efficient: Collective training is more likely to cover universal topics "that everyone should know" like common endgames for example, while opening theory will at most be dealt with very superficially (after all, everyone has to agree on the topic, and it's unlikely they will all like the same opening). This way, one can use the training sessions to fill the most important gaps not covered by the opening book, and use the opening book to fill the gaps of the training sessions.
This third group will most likely not get as good as the first group, but good enough for their taste, with considerably less effort. And I'd argue that it outnumbers the first group, and is thus more interesting for publishers.
I think it is because it is a lot easier to memorize some opening moves than it is to analyse positions. People are lazy and want to be told what is slightly better for White or whatever. And hey, they can survive the opening and look like they know how to play. They might even win a game without having to think for themselves!
Opening and repertoire books are popular because if one doesn't have a good beginning how is a good, playable middlegame or endgame to be reached?