I have spent a long time in ecommerce and follow the results of a bunch of public ecommerce companies.
It seems to be that Google basically collects the whole profit margin. Companies will do this to keep growth as high as possible to justify their high market caps and hope that they can eventually scale back on advertising and keep their customer base.
100% this! You are even required now (as an advertiser) to send so many metrics to Google for the algorithms to work they know everything about your business. The entire system is now engineered to extract the maximum possible value from the advertiser.
People complain about the tracking of visitors, but the tracking of advertisers own business is equally as abusive.
It seems to be that Google basically collects the whole profit margin. Companies will do this to keep growth as high as possible to justify their high market caps and hope that they can eventually scale back on advertising and keep their customer base.