And then every machine has a switching power supply to convert this to low-voltage DC, and then probably random point-of-load converters in various places (DC -> AC -> DC again) for stuff like the CPU / GPU core, RAM, etc. Each of these stages may be ~95% efficient with optimal load, but the losses add up, and get a lot worse outside a narrow envelope.
You could feed your servers off fat 12/24/48 volt supplies but with how much power a modern server can pull you're already converting in bulk even if you don't do that, limiting the potential advantages. For running CPU/GPU/RAM, there is no other option. When you need hundreds of amps at 1-2 volts, you convert that centimeters away if at all possible.
A datacenter using DC distribution is still using high voltages and stepping them down in layers. The hassle it avoids is in other aspects of power delivery.