Because no single receptacle is expected to max out the circuit.Why is it acceptable to install 15amp outlets on a 20 amp 12 awg circuit?
15A = what it can deliver to one particular plug, connected to the socket.Why is it acceptable to install 15amp outlets on a 20 amp 12 awg circuit?
A 1A lamp probably has a 18 AWG cord (max 10 amps) or a 16 AWG cord (max 13 amps) and no internal fusing. A high resistance short may heat the cord to cherry red without tripping the breaker. A hot cord can set carpet, drapes, and loose papers on fire. Happens on power strips too. We allow it because it makes this things economical, but I wouldn't say it's inherently safe.Similarly low power loads are _designed_ to be safe with a 15A plug configuration on a 20A circuit.