But apparently it's not easy to manufacture; it has to be the right concentration (there are various formulations) and pure (of impurities and germs). Amazingly, the whole US gets its bag of saline from only 3 manufacturers (my observation has been that all of peninsular Malaysia is supplied by Ain Medicare). Apparently Hurricane Maria jeopardized the American supply as manufacturers can't simply ramp it up; interestingly 1 reason for this is the high barrier to entry as the hospital groups' purchasing power ensure that they buy saline at the absolute lowest prices (only the companies with the lowest costs win).
Interestingly, the saline crises has forced American ED's to stop being lazy and do the right thing and encourage oral rehydration. Despite good evidence that it's better than iv fluids (both in terms of efficacy and cost), we still stick to iv fluids for what can only be described as "laziness". There's just nothing easier for the nurses than putting that iv line in, spike that bag of saline, hang it up, and continue with ward work instead of the kind "Western way" of encouraging patients to drink that solution of electrolytes; imagine if it was a typical Asian parent instead of that nurse instead. And if the patient can tell us that the bag of saline has just finished, all the better as now you can simply chart it as 500 ml (or 1 L) in!