Granted, the decline in sperm count is caused by something, but in relation to impact on behaviors, the decline will cause (as proxy) changes, and of those changes could be the increased medication, for example.
It may be the obesity decreases sperm count, but sperm count is dropping in people who are not obese. More than a decade ago there were reports on studies where the authors made simple extrapolations that sperm count would be zero by 2050, but these simple extrapolations are holding true in today's trends.
Some studies will bin people by BMI or some metric but fail to do any analysis on whether people aren't fatter within the bins. E.g. if the bell curve shifts right, the average weight of people within the slimmest band will still be heavier than before; even if the maximum BMI/weight is still capped at the same upper bound. And the deltas on sperm counts within healthy weight ranges are very small in most studies to begin with.
edit: searched in the past; not the few minutes since your comment*
Now present your evidence.