In addition to what Bogdan stated, Plarium's quest to encourage PvP has led to mechanics that favor attack over defense. The most obvious example is hamlets, where players are expected to expose their defense with no defense bonus in order to get small amounts of resources.
Beacon massacre is also an event that heavily favors offense. Its not as obvious, but here's why. The biggest disincentive to hit a beacon that is sufficiently stacked is that you may be able to topple it, but you'll suffer big losses yourself, making it an expensive victory. When a beacon massacre rolls around, 90% of that disincentive is removed. Now, players can throw their whole offense at a beacon in softening blows for the hammers and be guaranteed to get the vast majority of it back. Hammers, the ones for whom 10% losses are still pretty big, benefit from this because it is so much easier to get softening blows, keeping their losses to a minimum as well. The attackers benefit massively, getting big XP, points for any PvP or beacon tournaments up at the same time as the massacre, getting a fast pass to gaining more wisdom levels, and being able to rank up their offensive troops. The defenders get these same benefits, but their beacon is taken and often ping ponged down to level 1, and if they had all their def in the beacon, chances are a squatter will have plenty of time to get settled in before the original owner gets their def back and can effectively hold it again.
Another factor that strongly favors offense is the removal of troops dying from food production being in the negative. There have always been ways for players to work around that force limiter, but the removal of the limiter altogether has allowed for the creation of super armies. Before the change, it was very hard for even strong players to solo a stacked beacon. One player's offense, or even 3 players' offense, were at a disadvantage going against a beacon stacked by a whole league. Now, with that limiter removed, there are players who can solo a heavily stacked beacon.
These changes to the mechanics have shifted what troops people feel they gain the most benefit from. Defense troops are more expensive to create (force gained vs res spent) and are often put at a disadvantage due to the changes to game mechanics.
Off the top of my head, the one mechanic I can think of that favors defense is War. Because of the way troops are valued, defenders often gain more points than attackers, especially in close fights. Of course, the work around for that is to just fireball players. Then you get the points without giving any away.