Why is that last number so high? Simple: shoppers who use search already know what they are looking for. Their shopping intent is much more pronounced. They are just checking availability and comparing prices. They need little persuasion to buy - simply a tool to do it.
If site search fails them, your customers will bounce en masse. Search failure on the most basic level means returning no relevant results, or worse - returning a blank page. Other things come into play where a good search experience is concerned too.
Site search - or navigation - is just the top of your sales funnel. After your customer successfully arrives at a page with relevant results, he'll need to narrow them down to a manageable pool. That is the second stage of a selling process.
He or she will then go to a product page, or multiple product pages, before adding something to cart. That is the third and fourth stage of his or her journey respectively. Finally, he or she will need to click on the cart and complete the checkout process.
And, in an ideal world, you'd want your customers to return. That is the ultimate goal of any ecommerce store, to have as many loyal customers as possible, because they are the ones who bring in the most revenue