We Need More Writers!
To understand what people want to buy on the trading post, you need to first really have a solid grasp on what kinds of rewards players look for in Guild Wars 2. I'll tell you right now, it's the same as most RPG's: players want bigger numbers.
Sometimes game designers don't understand this. They add interesting mechanics for dealing damage that are often better than a higher base damage amount, but we players still favor seeing bigger numbers over efficiency.
Since Guild Wars 2 isn't all that difficult, you can get away with loading might and critical hit chance/damage for the vast majority of the game. It's not until you start doing group dungeons that having a little vitality and toughness becomes necessary.
So it's no surprise that leveling characters buy more of the might focused gear than at level 80. Sure, there are those that value condition damage, vitality, toughness, etc while leveling, but they are in the minority.
That is why I sell more rings with the word "might" in them than any other kind. It's also why "force" weapons sell so well to leveling players. We RPG peeps love us some bigger numbers.