While both types of removable media represent a risk of malware, a USB device represents a very real electronic threat of damage to equipment. You can easily in

While both types of removable media represent a risk of malware, a USB device represents a very real electronic threat of damage to equipment. You can easily inspect a CD-ROM or DVD disc and confirm that it is what it claims to be. You cannot inspect most USB thumb drives without destroying them, and they could be disguised keyboards, keyloggers, wireless exfiltration, or device destruction devices. I am really sort of annoyed by the step backwards we've taken from tapes and optical discs into "this really smart device that happens to store data wants to interface with as many computers as possible". It's icky for those who instinctively understand and practice good infosec hygiene.