Why tb and other communicable diseases have increased dramatically in the last few decades.?

They haven't: This is a misconception. Throughout the world, infectious diseases like tuberculosis, malaria, other parasitic diseases, and so on have become a lot less common over the past century, especially since the 1950s. HIV/AIDS is an exception, and TB and other problems are still extremely important and dangerous in some areas. But all in all, communicable diseases are in the best control in history.