Howdy Negin Hadisadegh,

This is not my main area but I enjoy learning about new things. I found this possible answer to your question on the site noted below as the source. Perhaps the right response to your question is that a spontaneous oxidation reaction "did not happen yet."

"One must be careful not to confuse the term spontaneous with the notion that a reaction occurs rapidly. A spontaneous reaction is one in which product formation is favored, even if the reaction is extremely slow. You do not have to worry about a piece of paper on your desk suddenly bursting into flames, although its combustion is a spontaneous reaction. What is missing is the required activation energy to get the reaction started. If the paper were to be heated to a high enough temperature, it would begin to burn, at which point the reaction would proceed spontaneously until completion."

I hope this helps,

Happy trails, Len

Source of quotation - https://chem.libretexts.org/Courses/University_of_Kentucky/UK%3A_CHE_103_-_Chemistry_for_Allied_Health_(Soult)/Chapters/Chapter_11%3A_Properties_of_Reactions/11.5%3A_Spontaneous_Reactions_and_Free_Energy

Many oxidation reactions have a negative free energy change, indicating that they are thermodynamically favorable. However, the fact that a reaction is thermodynamically favorable does not necessarily mean that it will happen spontaneously. The Gibbs free energy change, denoted as ΔG, is a measure of the spontaneity of a reaction, but it is not the only factor that determines whether a reaction will occur.

The Gibbs free energy change is related to the equilibrium constant of a reaction, which is a measure of the relative concentrations of the reactants and products at equilibrium. A reaction is spontaneous if its equilibrium constant is greater than 1, meaning that the concentration of products is greater than that of reactants. A reaction with a negative Gibbs free energy change will have an equilibrium constant greater than 1, and thus it will be spontaneous.

However, even though a reaction may be thermodynamically favorable, it may not happen spontaneously due to kinetic factors. Kinetics refers to the rate of a chemical reaction and how fast it occurs. A reaction with a negative Gibbs free energy change may not happen spontaneously if the rate of the forward reaction is slow or if the activation energy required to initiate the reaction is high.

Therefore, the Gibbs free energy change and the equilibrium constant of a reaction can indicate whether a reaction is thermodynamically favorable, but kinetics, including the activation energy and the rate of the reaction, must be considered to determine whether the reaction will happen spontaneously.

The distinction between thermodynamic spontaneity and observable reaction rate is clearly explained above. Thermodynamically, 'kinetic obstacles' are regarded as 'constraints'.

Part of the confusion in learning about this subject is caused by the different meanings of 'spontaneous'. Thermodynamic spontaneity is defined in terms of Gibbs Free Energy change but in everyday language 'a spontaneous reaction' is also used to mean a reaction that proceeds 'on its own', as when phosphorus burns in air.

One last point. Just because Gibbs Free Energy is negative for a reaction A to B, does not mean that B to A does not occur spontaneously at a microscopic level. If we imagine that we start with pure B, some B will form A and this will be true even if the equilibrium constant for A to B is large. The practical manifestation of thermodynamic spontaneity is macroscopic. A negative GFE change simply means that the equilibrium constant is greater than 1, but no matter how big it is, there will always be a small concentration of reactant at equilibrium.