Why is star formation more likely to occur in cold molecular clouds than in regions where the temperature of the interstellar medium is several hundred thousand degrees?

Stars can form when gravity which pulls things together exceeds the local pressure, which tends to push atoms apart. Pressure is higher in hot material and lower in cold material, so colder clouds put up less resistance to gravity and can collapse more readily. Also, at lower temperatures, molecules form. Because molecules are heavier than individual atoms, they move around more slowly and can congregate in a small volume of space, increasing the local matter density and thereby the local gravity.