I don't deny that. It's just that so many companies have so much inefficiency else where that addressing resource inefficiency has too low a marginal return.
One really does not want to saturate a fleet of servers to a point where random faults and broken SLOs are popping up all over the place. That’s first and foremost the main reason datacenter utilization is low.
Edit: sentence fixing
Surprising because one of the driving forces behind accelerating adoption of on-demand IaaS and various PaaS like Serverless is that too many expensive server resources lay idle. According to James Hamilton, chief Data Center architect at AWS, server utilisation remains very low (10%–15%) despite servers being the most dominant cost of building and running a data center (which is to say, folks pay through their nose for servers yet those are under-utilized by a huge margin) [0]
[0] https://youtu.be/dInADzgCI-s?t=535