Could it be because microservices and so-called "server-less" have been sold as cost-saving measures that increase the business' flexibility and decrease capital investment?
When... in reality a single deployed Docker container is way more manageable than a distributed system constructed with "lambdas" and requires fewer engineers in the long run?
What I'm trying to say is that FAANG cargo-culting is only part of why developers choose to build solutions that scale larger than they need. Another large part is the cloud development ecosystem writ-large and the consulting culture that has built up around it.
It's the same exact thing: most of the people do what is considered a "best practice" just to avoid any type of annoyance when something will break.