The primary goal of VSV's is to match pumping capacity of the front vs back end of the compressor. At low rpm, the front end tries to pump more air than the back end can handle, so the control system closes the front-end VSV's to re-match the stages.
And in so doing, the AOA of all the front-end airfoils is reduced to stall-free levels. Using a vector diagram, I could demonstrate this effect - reducing AOA on both rotor blades and stator vanes - but so far I have not found the vector diagram online.