The Charama Shloka graced by Bhagavan Sri Krishna in the Bhgavad Gita alone is part of the Rahasya Trayam. But don’t the Varaha and Sri Rama charama shloka-s have this sort of recognition?

It is not that both Srirama charama shloka and Varaha charama shloka do not have any recognition; Swami Desikan has authored Rahasya Granthams for these two charama shloka-s – “Abhaya Pradhana Saram” for Srirama charama shloka and “Rahasya Shikhamani” for Varaha charama shloka.
In the Rahaysa Trayam, since it is a VidhAyaka mantram, Srikrishna Charama shloka is part of it. We can notice from the Rahasya granthams that other two charama shloka-s are also treated on par.