LL, steroids are reported to turn off the signal to grow to your bones. Apparently kids who were growing and given steroids stopped growing when they were expected (based on the size of their parents) to continue to grow.
The Hormones in our food you refer to are most likely BGH (bovine growth hormone) in milk and milk products which can have the same effect as HGH, causing a person who is growing to grow taller and bigger. There are reportedly other hormones and compounds that can have effects on your body that are similar to hormones (mostly I have heard them compared to estrogen, but the media gets these things so wrong, who knows if there is any truth to it).
I have read another theory about how, when there is an abundance of food available to a population, each generation will get larger as part of the natural evolution of the species (or perhaps not evolution so much as the expression of less active genes over several generations). In contrast, where animals are in a situation of limited food, each generation tends to be smaller than the last, and you can end up with populations of pygmies as has been observed on certain small pacific islands.
So to answer your question, it is anyone's guess, but there are theories that carry some weight, that we can use to try and understand the trend you describe.