I think a lot have things going on with their liver and gall due to years of poor diet and lifestyle, did a cleanse, undigested food came out, and they misdiagnosed themselves. Fatty Liver disease has similar symptoms to flukes.
A lot of people also seem to have anxiety problems and phobias of bugs and things which could explain a lot too. Those are real health problems that need to be taken seriously and addressed or these people will continue wasting money and potentially due harm to their bodies trying all these medicines and cleanses chasing their tails with something they don't even have.
I myself would much rather hear the news that I have a phobia rather than actually having parasites or other creepy critters inside me moving around.