They are neither "customer" nor "product", they are suppliers, both of information which Google uses to assemble their targeted advertising delivery product, and of the actual advertising page impression opportunities.
They get less individualized attention then either customers or many other kinds of suppliers because there are lots of suppliers of the same inputs and the marginal value of each one of them to Google's business is very, very low, such that spending significant resources on direct support would very quickly turn them into a net liability.
They are customers of google search in that they buy search results in exchange for screen real estate and suppliers for the reasons you stated above. Google cares deeply about satisfying their search customers because they are also the suppliers of page impressions and personal information.
They get less individualized attention then either customers or many other kinds of suppliers because there are lots of suppliers of the same inputs and the marginal value of each one of them to Google's business is very, very low, such that spending significant resources on direct support would very quickly turn them into a net liability.