Why is my coolant light on even when I replaced almost everything?

Why is my coolant light on even when I replaced almost everything? Hi guys! I’m a women, I don’t know much about cars. I just had my radiator, radiator houses, radiator fan, water pump, thermostat, and coolant all replaced. So my question is why is my coolant light coming on?? I checked it… it wasn’t low, the light came off? But I’m afraid… because I had a lot of stuff replaced for closed fo 3000$