Current limiting circuit operation
It balances around the voltage drop across R1.
Q2 doesn't just suddenly turn fully on.  As current through the load increases, the voltage drop across R1 increases...once it gets high enough (around 0.7 V) Q2 STARTS to conduct.  At low enough currents, this transistor is just barely conducting current.
Once Q2 starts conducting it starts reducing the base voltage on Q1.
It stays in equilibrium.  As the current goes down, so does the R1 voltage drop, so Q2 conducts less, so Q1 lets more current through.