Because the base of the transistor is unbiased! In a cut-off state! There is no current in the circuit! When you use a multimeter to point AB, it is equivalent to adding the internal resistances of the meters at both ends of AB! At this time, the power supply forms a loop through the internal resistance of the meter and the LED! Rod tube is trying to connect! So it will conduct electricity! But its forward pressure drop is very large! About twice as much as ordinary diodes! That is 1.4 volts or so! In this way, the partial pressure of the voltage across AB measured by you is about 1.6V!

Because the circuit impedance is very large! The current is not enough to light two LEDs!

The voltage across BC measured by you is zero! That's because the transistor is off at this time! There is no current in the circuit! Nature is to divide the pressure!

Both ends of AC are power supply voltage! 3 volts!