Who needs autoscaling? I mean this as a serious question. Has somebody a real story where autoscaling helped out the company or product? If you have the hardware resources, why not just scale up from the beginning on? If you do not have the resources, you need a lot of money anyways to pay the upscaled rent afterwards.
I'm not sure if this answers your question but the last 2 companies I worked at (~7 years) both had very clear traffic spikes 9a-5p US east coast hours on weekdays. My current place actually sees more than 20-30% drop sunday nights compared to monday morning, and it's constantly going up because we have a lot of American enterprise customers. Maybe I misunderstood your question but is there a case where you can keep…
Colo providers charge by the [rack with given network port size and power delivery], so unless you literally host on premises which almost nobody does even when they talk about on prem, once you get outside of a cloud environment it is rare for it to pay to shut down servers unless they'll be down for a long time. Maybe there'd be a business there for colo providers to offer pricing that incentivises powering down machines (almost all modern servers have IPMI, and so as long as you provide the trickle - relatively speaking - of power for the IPMI board you an power the servers down/up over the network on demand), but it's not the norm.
The problem with these traffic spikes you mention is that "everybody" has them, and the overlap is significant, and so they're priced in because the cloud providers needs capacity to handle the worst overlap in spikes, plus margin. 20%-30% drop is way too low to cover the cost gap between even managed servers with a huge capacity margin and most cloud providers. I've worked for a lot of different companies where we've forecast our capacity requirements, and the graphs look almost identical. Sometimes shifted n hours to account for different in timezones, but for a lot of companies the graph is near identical globally because of similar distributions of userbase.
(If you do think you can do scaling up/down for daily spikes cost effectively, you can typically do it even more cost effectively by putting your base load in a colo'ed environment, and scale into a cloud environment if you hit large enough spikes; the irony is that in environments where I've done that, we've ended up cutting the cost of the colo'ed environment by cutting closer to the margin and end up almost never end up scaling into the cloud, but it gives peace of mind, and so being prepared to use cloud has made actually using cloud services even less cost attractive).
In practice, most places - there are exceptions that makes good use of it - just set up autoscaling so they don't need to pay attention to creeping resource use. Which is rarely a good use of it.
There are good uses for autoscaling, but it's very rare for day/night or weekend/weekday cycles to be significant enough that it isn't still cheaper to buy enough capacity to take all or most of the spikes (but having the ability to scale into a cloud service might mean you only buy just enough for the "usual" weekday cycles, or even shave a little bit of the top, instead of buying enough for unexpected surges on top).