This is an interesting question, and I don’t think it has a simple answer.
My thought would be that, rather than inventing what appears to us to be a perfect scenario, and asking why the texts don’t live up to that, we look at what the actual scenario was, and see how the texts emerged from that.
Consider two approaches to preserving information. One method is to lock everything down, and ensure everything is perfect within that limited sphere (like the Brahmins did with their secret transmission of the Vedas). The other is to open it up and spread it everywhere (as the Buddha did with the suttas). Call it Apple vs. Linux. Or Britannica vs Wikipedia. (When was the last time Britannica got in the news? Probably when they criticized Wikipedia for inaccuracy. Apart from that, they have become culturally irrelevant. The next time they get in the news will be when they announce that they’re closing down.)
In the closed garden approach, you can guarantee a greater fidelity with more constrained content. But you also lose something: and we don’t know what is lost, because it doesn’t exist. Yes, the Vedas are preserved, but what is not preserved? The more intensive the process of preservation is, the more resources it takes, and the less can be done. More quality, less quantity.
With the open garden approach, we scatter the seeds to the four winds, and they take root in multiple soils. Your control over each element is less, but it’s far more resilient (Buddhist texts are available in multiple languages across Asia, the Vedas in Sanskrit in India only).
Is the quality of user-facing apps better on Apple than Linux? Probably. But which wins? Linux is installed on orders of magnitude more computers (1.5 billion on smartphones alone), and will outlast any other OS in existence.
So much for the philosophy. But consider also the social context. The Buddha taught in multiple places over 45 years years. Everywhere he went, different people were remembering, learning, reciting, and re-telling his teachings (remember, the difference between “giving a dhamma talk” and “reciting a sutta” was far less then than it is now.) Much of what he said was the same, some of it was different. People were also travelling about, taking “suttas” with them, sharing them and learning them from each other.
The key to this apparent chaos is repetition. The Buddha must have used repetition widely in his teachings (as any good orator does). That means there is a partial overlap between different teachings. Patterns match up. In that way, the important themes stand out, while the individual details recede.
After the Buddha died, there was a twofold tendency. We know that through the Councils there was a centralizing tendency; large groups gathered together and attempted to standardize things. We know how that works out.
At the same time, there is is a decentralizing tendency: mendicants are wandering, mixing freely, moving into foreign countries, forming monasteries with their own dialects and teaching lineages.
The freedom to adapt, translate, and improvise lends a flexibility and a dynamic to the community. As another metaphor, consider DNA. DNA is able to preserve information with astonishing fidelity for millions of years. At the same time, though, mutation is essential. Imperfection is what allows the adaptation to new and changing environments.
What happens when two different organisms with slightly different DNA co-exist in the same environment? They compete. And may the best organism win!
The same thing happens when there are two different versions of the same text in the same cultural environment. There is comparison and competition; it creates a dynamic, an interest. It gets people talking. (In the sphere of social activism, I have heard this as a piece of advice. When submitting information to governments or other organizations, give everyone a slightly different version. Then they start talking about why it’s different!)
