They are building custom hardware and a lot of it so they get a bit of special treatment from Intel.
You engineer the thermal paths and better control how you get rid of heat. You tweak the board layout for the best performance of the chipset and CPU and run closer tolerances on voltages and clock frequencies while keeping it small. Buying in bulk also lets you customize the chipset and CPU packaging to get you better performance/watt and higher density by eliminating all the "fluff" stuff you really don't want on the cloud machine. Who needs all those USB controllers, PCI-e busses, and sound cards you find in your average server chassis in a high density server farm that just take up space and suck power? Just give me a couple of NIC's, a SATA connection and a serial console and a way to reset an individual system and I have what I need to stand up an OS and grant somebody external access to it.