Share 'Making a new neck.'

I'm considering building my first guitar and have looked into guitar kits from Stewart MacDonald. But being the kind of guy that prefers to do things the hard way, I want to build some of the parts myself - partly to save cost and partly to make it my own. My question is; Why do guitar necks tend to be made from a single piece of mahogany? It seems to me that it would be cheaper and less wastef…