Ask HN: Why can't a startup sell saline to hospitals?

So saline is 98 USD a litre in the US. What are the barriers to entry in this market? Why isn't someone else making purified saltwater and charging 49 USD a litre instead, halving the price and still getting an insane margin?

Pardon my naivety about the US hospital system, I'm not in the US. But for all the discussion around health care in the US, I haven't seen anyone address the lack of competition here.