The point was not that it's hard to do. It's that it's hard to do at a price that makes it competitive with renting a dedicated server.
From the DC perspective, the biggest costs for providing colo are power, AC (which is mostly power), network and real estate. Supervising rack access is a very small line item in their accounts.
As for power, and network, it's often charged separately, and you will still find the 1U vs. full rack difference then. Sure, you can to some extent perhaps assume a slightly lower load factor for customers that rent a full rack, and that may contribute too.
But the point remains: The person above me should not be surprised that renting space by the 1U slot is expensive.