Wasm is essentially a CPU in the browser. It's very barebones in terms of its capabilities. The DOM API is pretty beefy, so adding DOM support to Wasm would be a massive undertaking. So why add all that complexity when you already have a perfectly capable mechanism for interacting with the DOM?

There's not some conspiracy that's stopped it from happening. Nobody, anywhere, has ever said "DOM access from WASM isn't allowed". It's not a matter of 'allow', it's a matter of capability.

There's a lot of prerequisites for DOM access from WASM that need to be built first before there can be usable DOM access from within WASM, and those are steadily being built and added to the WASM specification. Things like value references, typed object support, and GC support.