There are 6 volts (2/3 Vcc) at pin 5 with your current setup using a 9 volt battery. The blue line is the voltage drop of the capacitor at pin 2:
View attachment 30727
As you can see, the pin 2 capacitor charges and discharges between 3 and 6 volts, using the upper comparator voltage at pin 5 for comparison. When the pin 2 capacitor charges to 6 volts, the output at pin 3 is set to off and the capacitor discharges. When the pin 2 capacitor discharges to 3 volts, the output at pin 3 is set to on and the capacitor recharges.
Since there is a steady 6 volts at pin 5, the low value capacitor at pin 5 quickly charges and then acts as an open, similar to leaving pin 5 unconnected. If you leave pin 5 connected to ground, current takes the path of least resistance and you get no output at pin 3.
edit: pin 5 is the upper comparator voltage, so if you ground it then that sets the upper voltage to 0.