When you tried to do that a few dozen times, and the outcome is always to build (and have to rebuild!) off platform, starting out off platform is the logical option.

Why should a developer learn 2 ways to do something when they could just learn 1. You are not improving the developer experience of the web by dictating that people have to learn 2. Either you make the native one capable enough to handle everything or you accept that people should just learn a javascript one that is capable of everything.