The carpet-bombing aspect of these attacks result in the attack spreading across entire network CIDR or network blocks. As many DDoS mitigation systems depend on specific host detection to monitor if the attack volume against a specific host goes above acceptable limits to trip an alarm, this type of attack often passes undetected and many times takes down all services in the network under attack.
The Reflective nature of these attacks causes additional issues as both the devices and services used as Reflectors struggle with the incoming flood of TCP SYN packets. Additionally, techniques which rely on sending challenge packets to detect spoofed sources, will in this case receive a reply from the Reflectors, resulting in the attack traffic passing through a dynamically created whitelist.