Mobile came on scene, which meant you wanted an API, which split web development into backend and frontend. At the same time, the powerful-but-crusty complexities of enterprise Java backend world, which Rails stood in opposition to, started to get more lightweight and fashionable answers in the Go/Kafka/gRPC/microservices scene. While a very convenient overall development experience, it didn't stack up as well when considered in isolation as either a backend or a frontend technology. Much of the Javascript integration it has today (Turbo, etc) came after people had already moved on.