Final answer:
The Company cannot cross the Misty Mountains through the Gap of Rohan due to the treacherous and dangerous trail. There are steep slopes, closed-in walls, and a leaning rock called Balancing Rock that could potentially close the passage.
Step-by-step explanation:
The trail through the Gap of Rohan is too difficult and perilous for the Company to use to cross the Misty Mountains. There are many steep hills, walled areas, and a menacing leaning rock known as Balancing Rock in the Rohan Gap. One of the characters, Venters, argues that if the rock is moved, it might fall and permanently seal the route.