All product pages are dynamic and generated on the fly. A page isn't refreshed, your store just updates the HTML code on the page. It allows loading new pages really fast.
The traditional way to track pages is to add some JS code to the page code which is executed each time you load a page and tracks your hit. If you try to use this traditional way, you will see that your browser will load your page just ONCE and all the other clicks in your store won't cause page reloading, and the result doesn't generate a hit. So your customer will open your store and see 100 products, but the stats will show only 1 view.
In order to overcome this limitation, we use Google Analytics API to emulate page loads. When you open a dynamic product page, the store sends a special JS request to Google Analytics saying that a new product page was opened. This way allows getting the exact number of views of your AJAX pages. That is why it's necessary to set up GA in your back-end to get the exact stats.