Lifestyle changes are one a reason. We used to be more active, and be out in the sun more which generates greater Vitamin D exposure. Having an indoor job, such as an office job, would definitely result in lower T levels without enough exercise and Vitamin D.
Another thing to consider is the abundance of microplastics. They are endocrine disruptors, and are shown to hurt T levels as well. Along with modern food processing ingredients like soy letchin showing to hurt testosterone levels, it really seems like we created this environment.
On another note, we know testosterone is intrinsically involved in voice maturity and facial hair, which partially leads me to believe it’s responsible for more of your appearance.
I think cancer is going up due to all the unhealthy crap we are exposed to. We all have cancer cells in our body, but I believe that some things we consume may aggravate those cells. Like we don’t eat as healthy as people once did.
Many of us consume fast food, soda, candy, and other junk more often than we should, and I think that constantly eating this processed food that we aren’t really meant to eat could have this type of effect.