Because the central pawns clash immediately, open games tend to produce free piece development, early tactics, and direct attacks on the king. They reward the classical principles — develop quickly, control the center, castle early — which is exactly why teachers recommend them to beginners.
Mastering open games builds the tactical alertness and development instincts that transfer to every other opening. The contrast is the 'closed game' (1.d4 d5) and the 'semi-open' games (1.e4 with a reply other than ...e5, like the Sicilian or French), each with a different strategic flavor.