Given its a constant operation which probably requires high speed interconnects. However it would be interesting to see how close in cost cloud is to a bare metal build.
While some cloud providers now have very high-speed, low-latency interconnects, they only scale so wide in a virtual environment. This is due to limitations in the physical datacenter space and the way node provisioning works on the back-end. If you truly need extremely wide, low-latency, high bandwidth interconnect for a large period of time, on-prem is still (probably) your best option.
We run a small clustered database across 8 nodes. Total cost for the hardware was ~ $3000 per node. Cost for a comparable node in EC2 per month? $1500. Even with co-lo costs for power and bandwidth, and buying 10gige switches it's far cheaper for us to host it in house than it is to use EC2.
That doesn't mean it's not useful, but it's still tens of times more expensive than using your own hardware.
Also, things are changing, but it is/was hard to ear mark funds for the cloud in a grant so spending the money up front was often what needed to happen.