Yes, but how is Mastercard encouraging me to spend more? In my day to day, it matters little which payment network I use since that’s abstracted away by the bank’s interface. What opportunity does Mastercard have to target me?

Presumably they could tell stores that you have your card on file with? (Only speculating; I have no idea if they or any other card network actually does that.)

Offering lower interests rates as a promo, higher limits, low interest loans, bonus points from certain brands/categories, offering new types of cards, etc etc

Read OP’s comment again. Mastercard is not a card issuer, they can offer none of the things you mentioned.

They sell your transaction data to Google. When merchants provide Level 3 information (line items), Google can now know exactly what you're actually spending your money on.

Then, Google can show you super-relevant ads, that might encourage you to spend even more.