Lights are normally wired using "Twin & Earth" cable. The earth wire in Twin & Earth cable doesn't have it's own insulation on it so if someone in the past has cut it right back you might not notice it's there. Have another look where the live and neutral wires come out of the cable sleeve.

On most plastic ceiling roses the incoming earth wire is connected to an outgoing earth (in a terminal block) but it's not actually used by the pendant. If this is the last light on the circuit there is no outgoing cable so it's possible the incoming earth was just incorrectly snipped off.

If you are replacing a pendant with a light that needs an earth then you may have to pull a bit more wire through the hole in the ceiling and strip back the insulation to expose the earth. The exposed copper earth wire needs to be sleeved with green&yellow sleeving before connecting it to the light.

If there isn't enough spare wire in the ceiling a new wire may need to installed.