>Why do doctors continually perpetuate this notion that slipping softly into death (palliative care, hospice) is preferable to continually trying to avoid it by way of riskier and riskier attempts at treating the root cause?

I think one reason is because they see people with terminal diagnosis take a beating from heavy medication like chemo and being unable to spend time with their family instead of just taking pain killers and spending their last months with family and friends.