raise the value and demand even more of a profit

When selecting two gathering professions, there is going to be some understanding that you won't be making gold from crafting, at least not on that character. Making them BoP is a good way of showing others that, you as a crafter, have made an awesome item for yourself. If you plan on selling the crafted item, it allows you to raise the value and demand even more of a profit.

As others have mentioned though,http://www.euwowgold.com/ there is always a chance they'll become BoA or BoE in the future but no promises. :P