Looks like it's primarily the "location" demographic that is actually different. Neither ad excludes any demographics for Age or Gender but the 2024 includes specific locations for advertisements. So maybe fewer people in Europe and elsewhere seeing American political ads, which I'd assume is preferred by the advertisers. I can see how that would compound to this effect; fewer valuable targets and more value per target.
(Another thing I notice is the ad run length. The 2020 ads ran for a single day (with over 10M views!) and the 2024 ads have been running for weeks or months. Not sure if that's relevant to the expenditure but it's interesting to note.)
2020: https://adstransparency.google.com/advertiser/AR123656109299...
2024: https://adstransparency.google.com/advertiser/AR104621681140...
Looks like it's primarily the "location" demographic that is actually different. Neither ad excludes any demographics for Age or Gender but the 2024 includes specific locations for advertisements. So maybe fewer people in Europe and elsewhere seeing American political ads, which I'd assume is preferred by the advertisers. I can see how that would compound to this effect; fewer valuable targets and more value per target.
(Another thing I notice is the ad run length. The 2020 ads ran for a single day (with over 10M views!) and the 2024 ads have been running for weeks or months. Not sure if that's relevant to the expenditure but it's interesting to note.)