Why would facial hairs from the top front neck area not be good grafts for beard transplant ?

Harvesting neck hair for donor hair source may not be the best or standard practice since neck hairs are not considered permanent hair.

Beard hair is an excellent source of hair for the balding area of the scalp.  The beard hair I transplanted in 2004 is still growing today.  Leg hair on the other hand grew well for years but then was lost later on in many individuals.  This is because leg hair on the front of the lower leg tends to disappear over time.  Beard hair tends to stay forever so I don't worry about it falling out prematurely.  Even scalp hair grafted from the back and sides of the scalp can thin with time so don't worry about using beard hair.  I suspect that many physicians don't have experience using beard hair and that is why they suggest it is not a good source.  It is a great source because it is coarse and curly and both factors add significant coverage value to the bald areas.The things you must know are that not all people like the appearance of their beard hair on their scalp so start with a test to determine how you like it, how you heal in the donor area, what the yield is, and how well it matches your existing hair.  Beard hair does tend to turn white before hair on the top of the scalp so be aware of this too.  If your scalp hair is fine and straight, your beard hair may not look as natural as you would like on the top of you head mixed in with the fine and straight scalp hair. 

Neck hair is known to disappear with age in some people so it is not a good donor source for a hair transplant. Stick with traditional donor areas so that your transplant will last.