Why would Elton John and William Shatner wear toupees when hair restoration is easily available?
Surgery is a personal decision, so I can’t speak for everyone… but I can make an educated guess. Hair restoration or hair transplant surgery is in essence about moving your existing hairs around. If you don’t have lots to move around you cannot cover a huge area of balding or achieve the look of a 16 year old fullness.
Moreover, many older celebrities with their financial success have had a hair transplant surgery 10, 20, 30 years ago when hair transplant surgery results were not the best. So with their fortune they depleted their donor hair supply and do not have enough donor to fix the problem. As a result, their only option is a wig and or toupee.