Hm... We'll get to that in a moment...
Back in 2002:
BETHESDA, Maryland—Total annual cancer cases will likely double in the
United States during the first half of the 21st century, with 2.6 million
people diagnosed with the disease in the year 2050, according to a new federal
report (see Figure). The major driving force for this projected increase is the
growth and aging of the American population, which will sharply increase the
number of cases even if the cancer rate remains constant.
http://www.cancernetwork.com/articl...-population-growth-aging#sthash.y9cqnEw1.dpuf
Obesity and Diabetes in Vulnerable Populations: Reflection on Proximal and Distal Causes
Ann Fam Med. 2007 Nov; 5(6): 547–556.
Likewise, people from low-income and minority communities, as well as immigrants from the developing world, increasingly visit physicians in North America with obesity, metabolic syndrome, or diabetes. Explanations limited to lifestyle factors such as diet and exercise are inadequate to explain the universality of what can be called a syndemic, a complex and widespread phenomenon in population health produced by multiple reinforcing conditions.
There certainly may be some other contributing factors, such as pollution, increasing (but barely detectable) amounts of prescription drugs in wastewater, and so on.
But the causes of some of these are already known, and in some cases, preventable. Cancer is a disease of the elderly, and other than early detection and treatment, not much to do about it. Most diabetes can be prevented by diet and lifestyle.