That is due to the fact that you are omitting something. The process may be natural, but it is so unlikely as to be "impossible". Chemicals form compounds in repeatable and predictable ways. Life changes the chemistry, by having catalysts available and proximal to the reactants. Without those conditions the compounds necessary for life are not formed. Competing reactions will destroy complex chemicals before they have the opportunity to be of any utility in the formation of life. In a nutshell, if the compounds are stable in the environment producing them they will use up the reactants in their formation and be extremely difficult to catabolize. If they are unstable in the same environment, they will be catabolized before they are complex enough to do anything. This observation is valid for dimers through the longest stable polymer. There are countless competing reactions contending in a wild lifeless "soup". The "astronomical" numbers presented for the improbability of the formation of the putative chemical antecedents of life only consider one type of reaction in the calculations.
Unless you can specify the exact chemical and morphological mechanisms by which life came to be, you do not have a believeable warrant to calculate the odds against it.