They are not produced in "just the correct quantities." Sometimes too much is produced and others, not enough. There is a feedback system of controlling the amount of enzymes and another on their activity that modulates activity within an oscillating range of function. There is no steady state.
Evolution would require that magically just the right mix of proteins and enzymes had to wait to be found in the same location before this could produce energy so it could reproduce. The chances of that happening are so extremely small as to be non existant. The universe hasn't been here long enough for such a remote occurance to have happened in a random fashion
Thinking like this results from a lack of knowledge and a lack of perspective. There are many versions of the cycle existing in nature. Many are not as efficient. This article is one of many investigating the origin of the Krebs cycle. Important is the statement:
Our analysis demonstrates that although there are several different chemical solutions to this problem, the design of this metabolic pathway as it occurs in living cells is the best chemical solution: It has the least possible number of steps and it also has the greatest ATP yielding. Study of the evolutionary possibilities of each one-taking the available material to build new pathways-demonstrates that the emergence of the Krebs cycle has been a typical case of opportunism in molecular evolution. Our analysis proves, therefore, that the role of opportunism in evolution has converted a problem of several possible chemical solutions into a single-solution problem, with the actual Krebs cycle demonstrated to be the best possible chemical design.
Many solutions to the production of ATP (energy for the cell) have been tried and are tried by various organisms. The Krebs cycle is prevalent as it provided an evolutionary advantage in efficiency over others. Key point - many solutions to the problem arose. Krebs isn't even the best - although it saved time by using existing mechanisms in protein production. Organisms using Krebs simply had enough of an advantage to reproduce and survive at a higher rate.
"Many solutions to the production of ATP (energy for the cell) have been tried and are tried by various organisms."
The connundrum is this: how was any living cell able to survive and reproduce before one of these processes became successful?