Your products at Google Merchant Center could have been disapproved. Also Titles & Descriptions make a lot of difference, so even if you have everything technically great, there maybe be very few impressions. If you launched Smart Shopping, which I guess you did, then you should also make sure you have remarketing tag with all events, as it includes dynamic remarketing & prospecting :) Also, what I do for my clients, is that I combine all the data and actually promote only profitable products. Saved money can be used to promote profitable products or for new acquisitions :) feel free to get in touch if you need some more help