Why does US have such a stupid system that seems to be abused to get people to accept plea bargains, which should be illegal in the first place, anyway? Is ther

Why does US have such a stupid system that seems to be abused to get people to accept plea bargains, which should be illegal in the first place, anyway? Is there any other country where they "stack" sentences on top of each other? Maximum sentence should be 20 or 25 years for 99.9% of criminals, and only the most cruel ones (mass murderers, etc) should get "life".