Facebook isn't "everyone". As I noted in the comment to which you're replying, there are people building and using Web Components.

Nothing about Facebook creating React prevents browser vendors from implementing Web Components natively. React uses other open standards (ECMA & HTML) which have existed for a decade previous to Web Components.

Web Components contains good ideas. React contains good ideas. You're arguing against people who are helping. Stop doing that.

Somehow I think the reaction would be different if Microsoft had done this, i.e., make proprietary competing technology instead of supporting an open standard. (Yes, React is proprietary--look into the patent rider issue.)