I don't think any sourcebooks speak of why X didn't try that. But don't try to rewrite the series, if you did that, there's always a way and Zero wouldn't have enemies to kill. Just Imagine how it'd go in the ZERO series scenario.:
It's the same reason why Ciel never told anyone. Initial believe that Copy-X was a proper replacement of the real X for many years. Neither X, in his new state, or Ciel, who is a young girl, can persuade the people of the world and the four guardians about their leader being a fake. After Copy-X declined, we have a situation where we have people that know of X's secret, people that doubt X, mass media propaganda, and the retirement of all that stand in the way of the utopia Neo Arcadia.
As of ZERO1, some of the Eight Judge Government doubted X's verdict of TK31, but they couldn't speak up, they couldn't doubt their hero X. For regular Repliroids knowing that X was fake would lead to a quicker death, for humans such a thought was simply unthinkable; X is the hero that to this day saves them from Irregulars. For Ciel and the resistance, they are trying to achieve that peaceful solution whilst living their lives protecting themselves from Neo Arcadia.
Add to that the following factor: the world goes into a crisis because they realized they lost their beloved X and would inevitably lead themselves to another Elf Wars by Dark Elf's release. Remember that the Four Guardians are well aware about the seal at Yggdrasil, and Harpuia also assumed power whilst hiding the defeat of X. It was Dr. Vile that revealed X's defeat to the whole world and was voted to be the new leader of Neo Arcadia on April 23.
As for believing in Cyber Elf-X. Ciel even doubted it's existence. For the Big4, who believe their X is a revival of the original, they were so heavily involved they couldn't start believing in Cyber Elf-X until after Copy-X was killed and Dr. Vile assumed power and Phantom was there to confirm the matter.
For X, whose powers are limited, having Omega breaking the boundary between the real world and cyberspace, is rather convenient.