Why A Product Search Engine And A Recommendation Engine Can't Replace Each Other

There is no denying that everyone who spends time shopping online has seen both search engines and recommender systems several numbers of times and the differences between both the engines seem fairly obvious. A search engine can be spotted easily -- it is a query box where you type in what you're looking for and the system shows a list of results. On the other hand, you also see some products has just appeared on your screen that is relevant to you, but you haven't requested for it; that's is the magic of a recommendation engine. But what makes a product search engine different from a recommendation engine? And where exactly deep learning, machine learning, and artificial intelligence come into the picture?