A lot of class players (as I myself am at the moment) have a tendency to overvalue material. Becoming accustomed to simply taking a pawn and then trading everything off (which fellow class players seem to be agreeable to), they see no possible reason to give away any of that not-so-hard earned material in the name of so-called 'positional considerations'. Checkmate is the only thing worth more than material to them. Perhaps this stunting approach to chess has something to do with the way they learned the game ("Queens are worth 9, Rooks are worth 5, Bishops and Knights are worth 3 but the bishop is a little better, etc...").
Here's a nice game I recently played that powerfully demonstrates why positional elements can be worth more material. I've done some annotating (sarcastically at times) so that what may be a foreign concept to some may become more clear.