The problem is not a shortage of astronauts, the problem is that it is very expensive to keep them alive. They are large and must be kept in an atmosphere in which they can breathe, they must be fed and kept in the proper temperature. Perhaps you might be okay with a couple of them being blown to bits every mission or so, but most people are not. Robots and specialized machines do not breathe or eat, can exist in great extremes of temperature, and only require electricity to function. If one gets blown up, they build another. They are expendable, and they can do almost anything a human can.
Maybe we could send a group of astronauts to Mars and back, but ti would have cost 100 times what the last expedition cost with robots.
The main reason to put man in space is basically romanticism, not scientific necessity.