Aren't the engine devs all part of the TC39 committee? I know they stopped SIMD in JS because they were mire interested in shipping WASM, and then adding SIMD to it.
I would say representatives of the engine teams are involved. However not involved enough clearly, because it should have been withdrawn waaay before now due to this issue.
It was also replaced with the Composite proposal, which is similar but not exactly the same.