For example Visa has an exclusive deal with oracle. So only oracle can buy audiences with visa data, and visa has super strict requirements and only builds them in house. If you say “I want users who purchased x product” the size must be 5mm users minimum (I think) and visa models it up using lookalikes/etc to 20mm+ users (maybe slightly off on sizes). Then it’s like $4 cpm to use at a dsp. Brands/agencies etc have to go through oracle to get visa data.