Why sell discs containing software that people can download for free?
In a word, “convenience”. Etch comes on 28 to 33 CDs and up to 5 DVDs (depending on the platform) which is over 20 gigabytes of software (double that if you want the Source CDs too) to download. Even if you had full use of a dedicated T1 line, which operates at 1.5 megabits per second, it would take you nearly 35 hours to download the images. (In all likelihood it would probably take longer because the download sites will have other traffic on their broadband connection.) Then you’d have to burn each image onto blank CDs and label them. Given the cost of a set of pre-made DVDs or CDs, you’d have to have a lot of time on your hands to make this worthwhile.