Hydras might avoid reproducing asexually in difficult conditions primarily because "the lack of genetic diversity could mean that all of the hydras die, depending on the situation."
In challenging environments, relying on asexual reproduction (which produces genetically identical offspring) can make the population vulnerable to threats such as disease or changes in environmental conditions. If a disease or environmental change negatively affects the genetically identical offspring, the entire population could be at risk. In contrast, sexual reproduction promotes genetic diversity, which can enhance the population's ability to adapt to changing conditions and improve survival rates.