Why does traction feel good when you have spondylosis?

Stretch the spine: With spondylosis the nerves exiting the spine may be pinched between vertebrae that have overgrowth of bone on them. By stretching the spine, you release the nerve. This opens the hole that the nerve travels through between the bones. This relieves the pain and some of the senosry issues too.

Traction: Spinal traction reduces the spondylosis and thereby reduces the pressure on the nerves and hence reduces pain.