Why did the Silk Road become unsafe?

Animals: Scorpions, coyotes, mountain lions, Yaks (don't eat humans, but can ram into them)

Mountains: You might fall off, There's a lack of oxygen, Animals could slip off easily, ringing in the ears, dizziness, Extreme heat and cold

Deserts: Sandstorms, your tent might move in the night, the sand dunes will move (you won't know where you are), Extreme heat during the day, Extreme cold during the night, many dangerous plants and animals, dehydration, mirages (can make you go crazy)

Flatlands: There are bandits, Your animals might overeat (and possibly die), you might oversleep from a lack of sleep (this can be dangerous)

Valleys: Falling rocks and boulders, Water will flood from the mountains, etc