Could also be that if you only purchase 1 item from a store you might forget the stores name, but referrals for large purchases are likely a big driver of their

Could also be that if you only purchase 1 item from a store you might forget the stores name, but referrals for large purchases are likely a big driver of their business so they want to make sure you do remember where you got this from in the hopes you can refer one person to make a purchase. A multi-thousand dollar purchase is likely worth it for an extra $15 in targeted ads to somebody.