They did exist, but technology hadn't developed enough to know what the different conditions were. Remember Victorian times, women had the vapours, people died from all sorts of catch-all conditions. IBS is far more than a dodgy stomach (I have a family prone to Crohns, believe me - the symptoms are hideous). I blame a lot of the allergies on people's obsession with cleanliness these days - kids aren't exposed to anything remotely buggy in their young days, all sorts of sensitivities come out later.
Better use that what, do you suggest? Illness prevention is what takes up a lot of GPs' time these days, trying to stop people dying young, sometimes from things they can (often) do something about, like obesity, smoking and addiction of Macdonalds.