People do learn to fast and deal with those signals. Once you are aware of what they are it probably gets easier. I've fasted before, by choice and via circumstance in less fortunate times in my life. Is it uncomfortable? Sure. But it is no punch in the face. It is something you can learn to push aside and handle the task. One can learn to go to sleep hungry, sadly.

And you mention exercise, that is an excellent point. Hunter gatherers might forage for 8 miles a day, while many peoples daily walking effort can be measured in a few dozen feet. Our bodies are built to be used. It is no surprise that when they are not, systems designed for a certain baseline load are no longer functioning as intended.