They couldn't: to form a W3C WG requires support of the staff and the W3C membership, and it was clear that there wasn't that support prior to the WHATWG's form

They couldn't: to form a W3C WG requires support of the staff and the W3C membership, and it was clear that there wasn't that support prior to the WHATWG's formation. I believe the original preference of those involved was to do it at the W3C. And indeed, Web Forms 2.0 was presented as a position paper by Opera and Mozilla at a W3C workshop in 2004, prior to the formation of the WHATWG, and voted down: https://www.w3.org/2004/04/webapps-cdf-ws/papers/opera.html https://www.w3.org/2004/04/webapps-cdf-ws/papers/opera.html