Multicloud makes sense once you get to megascale where you have a dedicated team negotiating with CSPs over your discounts. If you can credibly flip a switch and move your multi-million dollar workload to a competitor, you can save big money.

This comes on top of the benefit that architecting for multi-cloud at that scale usually forces you to simplify/rationalize/automate ruthlessly and so is probably beneficial for a "mature" org with lots of cruft anyway.

That said there may only be a few dozen companies in the world where this makes sense. I happen to work for one, but most engineers don't. Even then, this is at the extreme right of the maturity curve, meaning that there is lots of lower-hanging fruit to pick first

Multicloud is just an inevitable reality--the default. The only time I have run into homogenous cloud architectures has been in large organizations and even then I was removed from the multi-cloud concerns because I was focused on a single product/service that was hosted in a single cloud infrastructure.

Full disclosure I work at a company attempting to address this very problem. - https://www.facets.cloud/multi-cloud-infrastructure So, what we do is, create cloud-agnonstic YAML files that can be plugged into any cloud. So an AWS RDS effortlessly transforms into a CloudSQL in GCP and a flexible server in Azure.

And this is possible because we follow an architecture-first approach. We have blueprints where you define your architecture, and plug that template to any cloud provider.