Apparently you either didn't bother to read or you missed this:"The couple raised more than $1.3 million via GoFundMe to come to the United States for that purpose."
It doesn’t appear that money is a factor in this case. It is possible that Charlie is too unstable to move, meaning that even with a portable vent and medical staff to transport him, that he would most likely die from being moved. Without being on his medical team that is impossible to know. It is the only reason I can come up with for them ( the hospital to not allow it)