Direct serves patients on the "doorstep of hospice."
A high mortality rate is to be expected.
But if Direct also saves a lot more patients at that very late stage of cancer than standard of care, then that makes it a highly successful treatment.
I doubt people are dropping out because they've given up on what you call their "crappy existence" since people motivated to enter a highly experimental trial are, by definition, fighters.
Even if they would have otherwise given up, the adverse side effects of Direct are nonexistent so the suffering to reward ratio makes this an obvious choice.
They're going to get injected with drugs if they go into hospice (including, as you said, morphine) so adding an extra injection at wide intervals (with no side effects) to the schedule is not going to reduce their quality of life by much even if it does nothing to help.