Dr Margaret Flynn said Dr Prana Das, whose trial ended when he was injured in a burglary, "should have and could have been prosecuted".
Her inquiry found care providers were "impervious" to older people's needs.
The CPS said there was insufficient evidence for a conviction.
Dr Flynn who reviewed the treatment of the residents of six homes investigated as part of Operation Jasmine, told BBC 5 Live the CPS' response to her report had been "insensitive and blinkered".
"I think it's both graceless and insensitive, given that families are grieving and are aggrieved. The outcome is that what we have are a host of unanswered questions," she said.
"Given the very slow changing gears that kept matters of Operation Jasmine out of the public eye for over sever years, their (CPS) very rapid response is graceless."
Lorraine Brannan, of the Justice for Jasmine campaign group, said relatives now wanted to meet the Director of Public Prosecutions, Alison Saunders, to find out why the CPS was not reconsidering the case.
"We thought they would at least have considered it," she said.
"To give an answer almost immediately was disappointing. Everybody's really shocked at the level of neglect but still nobody is accountable."
The family of Daniel Rowlands, 86, who lived at a former Southern Cross home in Caerphilly county, which was not investigated as part of Operation Jasmine, came forward to highlight issues at the home following an appeal by Dr Flynn.
His daughter Julia Matthews secured an out-of-court settlement after suing the firm for clinical negligence over his treatment there.
She said her father, who died in 2009, would scream in pain caused by pressure sores on his feet, with the bones visible.
"No one will stand up and say, 'Do you know what, I am the one that caused that problem. I am to blame.' My father went through physical and mental torment," she said.
Police decided Mr Rowlands's case did not meet the criminal threshold for prosecution but Julia Matthews also wants that reviewed.
The author of a damning report into alleged abuse at south Wales care homes has criticised the Crown Prosecution Service for refusing to reconsider criminal proceedings.