@cicerone imposter,
It is easy to ignore if you are not a hospital - they cannot in case it is a patient that requires important medical help. Unfortunately they can not risk and not answer a call and like Chai stated - if you have a loved one in the hospital or in medical care - again you not going to risk not answering the call because it is an annoying robocall or sales call.
My kids were away with family on a trip - and we have family members all over the country - some of which have serious medical issues. If I see a call coming in from a legit medical center, I am going to answer. And seeing there was a call with a message (at the time I had not listened so it is no way that you see it is a hang up) - I am worried.
Fortunately for me it was more a moment of angst until I was able to verify it was a robocall from the leukemia society (or something like) and not that they did not want to leave a serious message behind, rather than a hospital having their phones tied up due to robocalls when they might need to help a patient.