An exposed location can put some cats off a tree, particularly if the bed sits in the middle of frequent activity with no quieter alternative. Exposure is about the cat's experience rather than just whether the furniture touches a wall. People passing close by, another cat watching the access route or a noisy appliance starting unexpectedly can all affect willingness to settle. Try observing the area from the height of the resting platform and note the usual traffic around it.
A more sheltered position may help, provided it does not trap the cat in a narrow corner or obstruct the descent. Keep the structure assembled and fixed as specified when relocating it. Do not cover the whole tree with loose fabric to create privacy. A properly sized hideaway or a different bed location may offer shelter more reliably while leaving normal access and ventilation unobstructed.
Look at the position from floor level: can people approach from several directions, and is the cat beside a busy doorway? Moving the item to a quieter edge of the same room may retain company while reducing passing traffic.
For product comparisons alongside this advice, see Velvet Nest and Silver Velvet Nest. The details below explain their sizes and uses.
Further reading: cats.org.uk; rspca.org.uk; cats.org.uk.
Velvet Nest
Silver Velvet Nest
AeroMat Chill Pad