The 16gb drives everyone has in their pocket also help.
Now that I am a professional, it's not that common for me to swap a hard drive.
Twenty years ago when I went to college (ugh, that felt weird to type) every dorm room had stacks of CDs in it... maybe an average of a couple hundred dollars worth per head. That music-selling bonanza just doesn't exist today.
I don't really have a strong opinion one way or another about whether this is a good or bad thing.
"Data note: The information in this press release is from NPD’s “Annual Music Study,” which is based on online surveys of U.S. consumers age 13 and older. NPD conducted consumer surveys between December 14, 2011 and January 3, 2012, and the final reporting is based on 5,799 completed surveys. In order to compare music acquisition across formats, NPD uses an equivalency of 10 standalone digital tracks for each CD album."[0]
I would guess they were counting all USB storage devices as "hard drives", so a large percentage is likely just USB sticks.
[0] https://www.npd.com/wps/portal/npd/us/news/pressreleases/pr_...