There can be too much of a good thing. The rapid expansion of available video ad inventory caused by Prime Video’s cannonball into the advertising pool is leaving its rivals soaked and increasingly desperate to sell their ad slots, causing a CPM (cost per thousand impressions) crash that advertisers have been eager for. With an upfronts market that has been particularly tight—driven by an advertiser push for a significant rollback on streaming CPMs—Disney has been notably aggressive. Variety first reported that the House of the Mouse has been trying to secure a volume of ad support across all its platforms by heavily discounting CPMs for Disney+, reportedly proposing up to 10% to 15% cuts. Exact dollar figures have not been…