AWS and other cloud providers are money printers because a lot of engineers are insanely tied into established patterns of doing things and can't think through things at a fundamental level. Ive seen company backends where their entire AWS stacks could be replaced by a 2 EC2 instances behind a load balancer with a domain name, without affecting business flow.
We did something similar to the work in the OP post at my work, we had a bunch of ECS tasks for a service, where the service did another call to an upstream service to fetch some intermediate results. We wanted to cache results for lower response latency. People were working to set up a Redis cluster. Except the TPS of the service was like 0.1.
Took me one day to code a /sync api endpoint, which was just a replica of the main endpoint. The only difference is that the main endpoint would spin of a thread to call the /sync endpoint, whereas the /sync endpoint didn't. Both endpoints ended with caching the results in memory before returning. Easy as day, no additional infra costs necessary.
But overall, personally, I don't hate the "spending innovation tokens to build a database is nuts" sentiment too much, because it keeps me employed at high salary while doing minimal work, where things that really should be basic CS are considered innovation.