Because compared to the alternatives, they significantly easier.
Attribution is arguably the biggest challenge in marketing. If you know that someone bought because of an ad you know you can spend more on that ad, if you know no one is buying from it you know not to.
With almost all digital marketing there's some amount of tracking, not necessarily of users, but of ads. When you make a sale you know which ad it came from. Now that's not perfect attribution, users might take a few views to click through, may go direct rather than clicking through, or may click through multiple different ads, but it's pretty good.
With non-digital marketing there's nearly zero information. Billboards, TV adverts, magazines, radio, even podcasts which are digital, etc. The way that attribution is done is based on times of day (did you get a spike after your TV advert aired), or it's based on location (did you get a spike in the area of the billboard). Sometimes discount codes are used for attribution (use code TUBE10 to save £10 on your next order), but those only work for some types of product and users forget more often than not (yes, even with discounts).
Marketing on Google, Facebook, affiliate marketplaces, etc, is all automatable, and more accurate, more precise, and therefore it's easier to understand marketing ROI, and easier to justify more spend.
Attribution is arguably the biggest challenge in marketing. If you know that someone bought because of an ad you know you can spend more on that ad, if you know no one is buying from it you know not to.
With almost all digital marketing there's some amount of tracking, not necessarily of users, but of ads. When you make a sale you know which ad it came from. Now that's not perfect attribution, users might take a few views to click through, may go direct rather than clicking through, or may click through multiple different ads, but it's pretty good.
With non-digital marketing there's nearly zero information. Billboards, TV adverts, magazines, radio, even podcasts which are digital, etc. The way that attribution is done is based on times of day (did you get a spike after your TV advert aired), or it's based on location (did you get a spike in the area of the billboard). Sometimes discount codes are used for attribution (use code TUBE10 to save £10 on your next order), but those only work for some types of product and users forget more often than not (yes, even with discounts).
Marketing on Google, Facebook, affiliate marketplaces, etc, is all automatable, and more accurate, more precise, and therefore it's easier to understand marketing ROI, and easier to justify more spend.