Because Satan and his world cannot force us to do anything against our will. Some have given in to this temptation by allowing their minds to dwell on what is bad.
فَٱلْبَعْضُ ٱسْتَسْلَمُوا لِهٰذِهِ ٱلتَّجْرِبَةِ لِأَنَّهُمْ سَمَحُوا لِعُقُولِهِمْ بِأَنْ تَتَمَعَّنَ فِي مَا هُوَ رَدِيءٌ .‏