Adam Treloar, Jaidyn Stephenson, Tom Phillips, and Atu Bosenavulagi were all offloaded to rival clubs last week, with the Magpies receiving well under market value in return.
"We were without realistic access to the free agency market with our salary cap being at its limit," Anderson said.
"We have had quality players expressing interest in coming to our club, interest we could not realistically pursue due to our cap limitations.
"This could not continue and so some tough and, frankly, painful decisions had to be made."