Sunk cost is/was my conclusion. At one firm in ~2013, advertising was bringing in $600k revenue per annum - we estimated a loss of potentially triple that (!) - but the response was apathetic. There was very much a reluctance to accept that the "advert management team" (yep, they had a team dedicated to managing the adverts, who had the duty of "managing" Google Ads) would need terminating, too.