Imagine a circuit in your home being rated at 20A. The wiring can handle a bit more. The breaker is 20A. If you plug in an appliance that draws 150A, the breaker trips. If the breaker didn't trip, the wiring would heat up and , potentially, start a fire. The breaker prevents more that 20A from flowing into the circuit.
Now imagine you plug a bunch of these panels into that circuit, along with the appliance. The breaker would still only allow 20A from the utility to flow into the circuit. The panels connect to the circuit directly, without going through the breaker. You might have 50-60A flowing through a circuit that is rated for 20A...
Result: fire...
