Why are there so many different distinct diseases in our world? What is the cause and effect?

Is it Heredity? Caused by Pollutants over time? If it is genetics? Could our generations before us have eaten badly? Ingested harmful pollutants? Coal Miners, War Vets, Arms manufacturers? Have we cause this? Spending more money each year on R and D and even more on producing so called cures. Building better testing devices… Radiation machines causing more harm to the human anatomy.
When will we finally stop talking and start acting? And make intelligent steps forward to prevent these diseases that effect all societies of humans.