The big ecom marketplaces do customer experience management in-house.
^^I think this is the biggest reason. Every website, call center, etc wants you to take a survey after your interaction.
I have done some online shops though.
Examples:
-Purchase and returns (I evaluated the packaging it came in, if the delivery came when it said it would, if it was correct and on the return end of it, if the system emailed me updates and if my refund was properly credited).
-Evaluating website ease of use
-Price comparison and page placement of specific search terms for two major ecommerce retailers
-Submitting an inquiry and seeing how quickly you receive a response.
Some retailers might value the in person experience more - did the cashier greet you properly, did you get upsold on something, was the store in good condition, were employees dressed and behaving appropriately, etc?