Why can't a facelift be reversed?

Thanks for the question.
A facelift generally will involve the removal of a segment of skin and addressing the underlying SMAS layer by cutting/stitiching or changing its direction to aid in the lift. Due to this very process, as you are removing tissue, it is not possible to reverse this as there is not skin to put back. One way of doing this would be by using skin grafts to replace the skin that was lost and reraising the SMAS layer and letting it sit without securing it in a higher place and this would essentially reverse the process but the results would be less than adequate and not something that I would advise. The scarring that develops through the process of a facelift would essentially negate this and would leave you with a substandard result.
I hope this helps 

Most face lifts involve restructuring (reshaping) facial and neck muscles and fascia (SMAS) which includes removal or tacking of this structure in the neck and face. Also, face lift involves removal of the skin in front and behind ears. It is impossible to entirely "reverse" face lift because of removed tissues and changes that have happened after surgery. However, some aspects of face/neck lift can be revised (corrected) to provide more natural look after face lift. 

Thanks for the interesting question. Most facelifts tighten the skin and underlying layers and involve removal of tissue. To reverse a facelift would imply releasing the areas that were tightened and adding tissue. However, the methods to add skin or soft tissue (i.e. skin grafts) would appear unsightly.  One of the goals of reversal would be to create lax tissues and skin but I am not sure if this is possible because through the healing process the underlying tissue will undergo inflammation and fibrosis. The tissue would not be as supple as lax skin and soft tissue associated with aging. I would not suggest reversing a facelift or attempting it. Hope this helps.