Campbell signed for Ipswich Town last week on-loan.
Holloway explained: "I spoke to my chairman and to DJ yesterday. It ended up a difference of opinion with us and them.
"My chairman was insistent on him coming for the rest of the season. We were going to take him until January, but my chairman thought that would have caused a big problem in January if DJ scored lots of goals.
"He didn't want another fight in January and wanted to secure the longer deal now.
"DJ chose to give himself the option to go somewhere else in January.
"QPR decided that's what they wanted to do too, so he's gone to Ipswich.
"I tried to get him, it didn't happen, so let's move on."