The fact which the questioner has to take into consideration is: Gita is a part of Rahasya literate alongside Upanishads, Sutras, and Tantra. Meaning, a literature that was kept between a lineage of Teacher (Guru) and closely recognized worthy student (Sisya). Why? Gita by itself is a summary that crosses many darshans (esp Sankhya-Yoga) of Sanatana Culture because it belongs to the Itihasa section. So reading it as if it's a textbook with word-to-word translation was never the intent. What is the proof?
Well, do we really think Gita was discussed widely in ancient times to the common public in open settings similar to Ramayana and the events across Mahabharatam and Puranas? Do we really things Gita was giving word-to-word pravachana in open settings without context during festivals. Don't look at today as the basis, think from ancient times? Do we really think a thesis like Papancha-Sara-Tanatra or Primary Upanishads or Brahma Sutras were given to the common public on open grounds?
So, Where is the source for this? Who pulled Gita to its prominence compared to other Gitas? Let's look at the history first. We have to understand that there were over 1180 Shakas of Vedic studies and implementation. Today we have only 14 Shakas out of which 6 are in practical implementation (continued oral lineage, Gov. of India has created a portal and has invited these families so that they can record their recitation). If we do the math, less than 2% survived after thousand years of invasions, displacements of families, loss of soil fertility due to drought, flooding, death of cattle, death of family lineage. Why is this important? It's important because the readers have to realize that each Vedic shaka (branch) has its own Upanishad. This Upanishad is the philosophical concept that surrounds the mantras laid out in the Samhita section of that school. They also emulate the implementation of these mantras with their respective stories in the Brahmana/Aranyaka section of this school.
Now we know history, how is this applicable to Gita? And did anyone do anything to save this Vedic knowledge?
Yes, a child prodigy at a very young age saw this. This young boy, walked the entire land of Bharat on foot multiple times and re-organized the entire Vedic essence. He collected various Upanishads (Veda+anta = Vedantas) belonging to various Shakas/Schools. Then he added Brahma Sutras and extracted Gita out of Mahabharata Itihasa. Then He took content out of Tantras and created various hymns like Soundarya Lahiri and gave a thesis called Prapancha-Sara-Tantra (The transcendental (Tantric) essence (Sara) of the 5 elemental creation(prapancha)). With this, this young boy before the age of 30 established 4 schools surrounding Bharat. He foresaw the loss of various Vedic Schools and gave this massive collection of literature that is extracted out of Vedic essence. 1000 years later many sectarian acharyas emerged and created their own subset schools specific to the diety (among the 5 major Dieites) of their preference.
Now a question back to the Questioner: Do we think that Gita is still a separate book that should go about with printed books with word-to-word translations given by each sect based on their own preference? The answer is a clear NO. There are two ways one can approach the Gita.
- Either read the entire Mahabharatam (from a non-sectarian translater like Dr. Bibek Debroy, or the image created by native scholars which are called Andhikaranam-reimage) and then read Gita as a part of its continuum.
- Read Gita as a part of Upanishad Bhashya given by the first person who gave it such prominence to being with. Again as a continuum to Upanishad and Sutra Bhashya.
Finally, does Gita stand separate from Vedas? Well, when we know how many shakas are lost forever, how much remains, how can one judge this, and with what? The only thing left from these shakas are the Upanishads. So either link it with Upanishad Bhashya or link it with Itihasa as a whole. But too much damage can come if read from a sectarian literature or as an individual's translation as a solo literature.