OpenRA

It would increase online and popularity of the game.
Does anyone know the reasons for her absence in Steam?

and?

As far as I know, the license agreement with EA precludes a Steam release of OpenRA. Certain features would be nice to have fully fleshed out before that point anyway, like translation support or finished single-player campaigns.

It makes sense that licensing issues with EA could block the game from appearing on Steam. I guess that also explains why the developers might want to polish things like translation and single-player campaigns first — so the Steam version,stickman hook whenever it happens, can be a full experience.
Still, it’s a bit disappointing for those of us who prefer Steam for everything. Hopefully, there’ll be some update or announcement soon.