Huge waste of CapEx for those expensive training GPUs if you can only use them 8 hours a day (same goes for all other data center hardware). Nevermind data availability and other hard problems if your DCs don't run 24/7.
You do spot pricing or preemptable instances at the margins to help maximize revenue while minimizing excess carbon.
I assume that most cloud venders are over-provisioning because their margins are so good that they'd rather overspend on inventory than miss out on revenue most of the time.
