Popularity, yes. The most famous Anime are the infinity shonens, like One Piece and Naruto. What is shame, there is a lot of good Anime out there which deserve more fans.
But I disagree about the lower quality. My experience with Anime tells me that Anime with lower episode numbers has a higher chance of being worth watching. And it makes sense. Many episodes = More money needed to do something decent, you know? That's why those infinity shonens have crappy quality animation and crappy other things. XD
With less episodes, they can focus the money on the animation, visuals, soundtrack, etc... Since the story usually is from some visual novel or game.
True. I'm guessing you're seeing this from the animation perspective?
Lower episodes DOES increase quality in animation sense, but it does not mean they increase in story and character. There are some who're taking the story & character raw/un-adapted to the animation world itself. Therefore, worsening the anime more than the original VN/game/story. (I'm taking "School Days" as an example (And due to the references of it I'm getting a lot behind lately...))