Because in the US at least the probability of you breaking your leg and going into medical debt then losing everything because you don't have insurance is far higher.
My daughter broke her leg just over a month ago. I have decent insurance and my out of pocket expenses were still close to $2000 alone with in network coverage. I think a lot of HNers are somewhat wealthy middle class+ with cash in the bank, or not from the US so they have no clue how out of control these kinds of expenses are.