We've always lacked understanding. However, it didn't feel like a bottleneck; in spite of lacking understanding, we developed huge, complex systems that became hard to maintain and that nobody understood completely.
Now we want to scale that orders of magnitude, but when we do that, we feel the pesky lack of understanding.
We previously worked around the lack of understanding by making the system gradually incomprehensible in small increments, upon each of which we observed it still working, more or less.
If the whole thing materializes in one day, that doesn't work; the approach is gone.
You can now bring into being something which statistically resembles the old kind of system that was iteratively evolved. But the thing has no such history. You can't go back to play archaeologist. It looks like something that would have had users, but it never did. It was never in production anywhere. Nobody ever submitted feedback, or a bug report, such that it was fixed or improved. There never existed a simpler version of it that several ex-maintainers understood perfectly; there are no such ex-maintainers and no such understanding. There is no documentation trail, or other historic trail if surrounding activity like discussions and negotiations which led to things being the way they are.