LiveView isn't meant to be a replacement for Angular/Vue/React. It is meant to address the many companies/projects that were once doing some light client side functionality with jQuery or prototype and have since gone full framework and are now finding themselves with a much longer time to implement what was once simple. The overhead that frameworks impose are meant to manage complexity but if the interactions are simple then that overhead is a liability.

Some people also just don't like JS so there is that.