Why are my defenders not MAKING?

Is anyone able to please tell me why, no matter what formation, tactics or player roles I use my forward players are ALWAYS marked but my opponents forwards are ALWAYS free and standing clear in the middle of the pitch?

Every time I play a through ball it is intercepted by my opponent or it just goes straight to my opponents player. But 90% of the time my opponent plays a through ball it goes straight to his unmarked forward who has a clear run to the goal because my defenders are nowhere to be seen?