There is no economic value in funding this backup plan by the private sector (which is defined by profits). Its not like they will "own" the new colony - unless, of course, if they actually do. I.e., if the corps are allowed to use those colonists raised as slaves for the corp's gains, then there would be economic value and hence, the private sector will attempt to do this.

Though i doubt that is ever going to pass, so the only alternative for this "backup" plan is gov't funded expeditions.