That money passes through several transactions. You're a customer of shops that are customers of manufacturers that are customers of Google. We don't generally treat customers of customers of customers as customers, so I'm not surprised that Google doesn't.

I suppose you could argue for some sort of tracking system that would give Google data to prove that you do in fact buy what you buy, so Google would know that you aren't a penniless hermit, customer of noone and source of no money. I can see some disadvantages to such a system though, and I think you can too.