They could have ignored the W3C, but losing in the W3C would have been a significant thing. It would have shown the web community is taking a stand against DRM.

They could have ignored the W3C, but losing in the W3C would have been a significant thing. It would have shown the web community is taking a stand against DRM. It could have helped further battles against DRM. Instead, by winning at the W3C, Google and Microsoft made DRM's victory as official as possible.