There is very little reason to need auto-scaling when you run on pre-purchased VMs/servers. You've paid for all the compute so you can run as many replicas as it can fit and you need to handle the projected amount of traffic.

There are no benefits to scaling down in this case. And scaling up won't help handle more load if you've already allocated all resources to running replicas. You need more machines, not more replicas on the existing machine(s).

It all comes down to simple, boring capacity planning and static resource allocation. Fewer moving parts results in fewer failure modes, hence more robust infra and less ops and maintenance work.