When I search for something on Google I often see links to only one or two website in the original SERPS above the fold. The rest is advertising. And sometimes Google Shopping Results.
Now what do people do in that case? Scroll down? Move to page 2?
No. They click the ads.
So from Googles perspective this makes sense - more money. Even if it means loosing a few users to other search engines.
This is especiall true for product searches. Often it's only the manufacturer above the fold - if you want to sell and want to be seen you have to advertise. This is a win win for Google. Searchers still find their products - not in the SERPS but in the ads - doesn't matter for them though. Satisfied users. Shops have to buy ads to be seen and pay money to Google.
So in my opinion showing multiple results for one site has only one reason: Block space in the SERPS, push other results down, increase ad revenue.