How come when I Search for a book (I only seach for a book because I would like the book and not because I have it and wish to post it) one of the options isn't to add it to my wish list?

If the order button is there it means the book is in the system. Only books that are not in the system can be added to the wishlist.

There is always the reminder list button, if you want the book sometime in the future, but it is currently available so you can add it to your wishlist.
 

I agree with Mistie.  I think the Reminder List will serve your purpose.  The wish list here is for getting in line for books that aren't currently available.

Also, in the book browser search there is an option to narrow the search to posted books only.  If you have that filter on, you will not be seeing any unavailable books that you could actually add to your wish list.

I think of the Wish List as a waiting list.  

Your question is eliciting different responses because it's unclear whether you want a book for which you've searched now or later. If you search for a book and there's no "add to WL" option, it means the book is currently available. If you wish to order it, you can do so. If you're not ready to order it now, you can put it on your reminder list. You can't put it on your WL because the WL is only for books not currently available. Folks use the reminder list for different reasons -- ofttimes to see how many copies of a book are posted, sometimes as an overflow WL, sometimes to keep track of books that they may want to order or WL in the future, or whatever.