- I seriously doubt that there is one, unified, conspiracy-theorist-satisfying explanation. Even if there is one, I seriously doubt that it will ever be aired in public to the satisfaction of conspiracy theorists everywhere.
- The mechanism appears to most probably include a combination of several factors, including some astroturfing, some incompetent programming and systems management, some misguided marketing and inventory-management bullshit, some inadequate training/preparation of customer-service droids and PR dorks, and the stupidity of making this into a "holiday weekend." All in all, this was a disaster of some kind waiting to happen... whether triggered with malice aforethought or otherwise.
- To the first-time customer, it doesn't matter whether there was malice aforethought involved; he/she won't get an accurate search result. This really does two things: It points out the idiocy of reflexive, black-box "sales ranks" as the primary ordering algorithm for search results, and it points out that the customer is not always right.
Most importantly, though, there's a structural cause-and-effect relationship from the positive feedback loop. Ultimately, the problem is that Amazon dominates a certain aspect of book distribution exacerbated by the holiday-weekend nonsense to an extent that strongly implicates antitrust issues. This is a result of the overcorrection in antitrust doctrine imposed by the Reagan administration, which chose to eliminate false-positive accusations of monopolization... no matter how many false negatives that policy engendered. The simple fact is that book distribution is an oligopoly, and Amazon exercises actual and/or potential monopoly power (such as the power to unilaterally set payment terms).
Some of the antitrust conundrum comes from difficult problems of market definition; one reaches a drastically different result for every aspect of book distribution for "category trade fiction with at least 20% of sales through chain bookstores" than for "all casebound books published". More of the problem, though, comes from the application of economic theories tested only on initial-endpoint actors in relatively clean marketplaces to midpoint and terminal-endpoint actors in the very, very messy real world. In short, we're dealing with economic theories of antitrust with similar value to the Laffer Curve: They are aggregate-behavior models (PDF) of theoretical behavior that are essentially untested in the real world. More precisely, quasieconometric antitrust models implicitly discount the endowment effect and presume actual substitution not just theoretical substitutability of every purchase decision based upon the characteristics of fungible commodities. And there is nothing more endowed, or less like a commodity, than individual expression.