What a very probing set of questions! You've uncovered Leon Battista Alberti's little secret. <i>On painting</i> is not more popular today <i>because</i> of the way modern artists feel about Alberti in particular. <i>On painting</i> was <b>the</b> body of work on painting theory, and as such garnered a lot of attention, including the unscrupulous eyes of the critics. These critics noted that Alberti himself produced no discernible master piece, or for that fact any piece worth noting. In addition to this, the most popular translation of <i>On painting</i>, the one translated into Italian by Alberti himself was literally almost read out of existence.