I agree the older version of Windows 10 can be hard to find.
I feel some buisnesses, schools, more tech savvy users and PC gamers may have old versions of Windows 10 just in case a PC game, software title, and hardware driver software/firmware does not work with newer version of Windows 10.
Some people may still burn Windows 10 ISO disc images to DVD-R to upgrade and install Windows 10 because DVD-R discs are more cheaper than a USB flash drive, or their older PC can't boot from USB drive. These users may have many versions of Windows 10 burned to discs or as ISO Windows 10 install disc files.
From My Personnel Experience
DVD or CD Rom clueless as they get damaged soon. In the past I got DVD ROM's for new PC's but they worked in the first few days and then dead. The companies are branded like LG DVD Rom.
For Gamer's DVD must be compulsory to install new games. I don't know the current DVD Roms how they are working.
