I don't think one should read much into them needing Wallet internally. Google needing to accept credit card transactions for the Play Store is almost tangenti

I don't think one should read much into them needing Wallet internally. Google needing to accept credit card transactions for the Play Store is almost tangential to the service: offering a supported API to 3rd party merchant-users for processing digital goods transactions. The latter involves risk assessment, underwriting, customer support, maintaining card association/acquirer relationships, so on.