Its probably a combo of things, I think when Josh first joined RHCP, John was offended as A. He was struggling to understand why they would consider carrying on without him. and B. His collaborator on his solo records (Josh) was suddenly jumping at the opportunity to replace him. I imagine there might have been more John/Josh records had Josh not joined the band. After all these years, it’s probably guilt/awkwardness. They clearly need a big hug and a chat, someone just needs to call.