No bookshop can stock all titles. No bookseller can keep current with everything that's coming out. If an Amazon discount and next day delivery aren't crucial factors for you, ordering from your local bookshop helps alert staff to new publications.
I ordered this, Compendium of the Occult by Liz Williams. One of the booksellers took a look when it came in and promptly bought their own. Sometimes they've added a copy of titles I've ordered to the shop's stock.