The motivation was edge and latency-critical use cases on a product I consulted on. Feature vectors arrived pre-formed and a Python runtime in the hot path wass a non-starter. You're right that for most pipelines the transformation step is the bottleneck, not inference, and Timber doesn't solve that (though the Pipeline Fusion pass compiles sklearn scalers away entirely if your preprocessing is that simple). Timber is explicitly a tool for deployments where you've already solved the data plumbing and the model call itself is what's left to optimize.