I feel like the process of adaption has become so commonplace in the anime industry that I'm fairly sure these anime are just made on reflex, 'because that's how it's done'. Like creating an anime adaption is what lends legitimacy to the manga, Light Novel, or game property. As if the property doesn't have merit or isn't 'popular' unless it has an anime, which doesn't make all that much sense if you really think about it. Maybe the producers see anime as just a high-budget advertisement, but I have to wonder if the animators/directors and writers and such could really tell you what the purpose of one of these animes is. As far as I know, the original Mangaka or author isn't really directly involved with these projects, so they're always working with somebody else's work rather than producing something that came fully formed from their own imaginations (though I'm sure plenty of them are fans of the properties they work on.) I'm probably wrong about this since I have no insider knowledge, all we can do is speculate really.
It feels like adaption in anime is about trying to blow through plot points as efficiently as possible rather than trying to take advantage of the strengths of the medium, which is somewhat of a shame, really, even if that's not their intention. Adaptions do work sometimes, though, if only because of law of averages... one has to work eventually.