Selling on Google Shopping is typically quite lucrative for 2 main reasons. The first is that conversion rates tend to be higher than regular search. This is because users on Google shopping are in "buy" mode as opposed to research mode. Also, in contrast to regular search adverts, the user can see a picture and the price of the product before clicking on the product. This means that users who click on a Google Shopping product (either in Google Shopping itself or from the search results page) are highly qualified and tend to convert at high rates.
The second reason that Google Shopping tends to outperform regular search is that click costs are lower than on regular search as competition isn't as stiff. This is because setting up Google Shopping is considerably more complex and labor intensive than setting up a standard search campaign.
The combination of higher conversion rates and lower click costs is a lucrative combination.