The DOM and JS are joined at the hip - the DOM APIs are designed assuming JS is used to access them, and the design of JS and some of its more “unique” features is partly because it was designed for use with the DOM

People choosing Flutter would say the uniformity of a canvas across all browsers is more valuable than gaining the inconsistently implemented web feature set.

JS is just so much more approachable than WASM. You can debug it on the fly, feed it to an LLM, there is no wrapper, it's just so much easier to tinker and work with it.