[_ttg]

Basically all these puzzles are trying to train your combinational vision and calculation. An important component of calculation is getting good at executing 'forcing' moves (moves where your opponent has only one or two plausible choices) which are more clearly illustrated in attacking positions or 'Mate in X' positions. Even though the most readily available material is from 'attacking' positions, this skill is transferrable to many other kinds of positions(e.g pawn endings). Defense on the other hand is often more vague with more than one optimal strategy and rarely forcing, so there's just not a lot of good material to draw from.