Becouse there is the chemical balance tilted, so only bacteria that are needed to make alcohol out of it will live through that. Things that would usually take over and do the rotting can't live there. Things don't rot by themselves, there is fungus and bacteria doing it, and they need usual environment to live. There is ton of CO2 created in that process, that taxes O2 away, that's main cause of death of things in this kind of basement, including people.