Here's why - DE is microscopiclly razor sharp - BUT - it will not work when it is wet. It works by slicing hard body insects that crawl over it - they are sliced open and dehydrate. (Internally, parasites are soft and slimy - not hard bodied.) When DE gets wet - from rain or body fluids - it "melts" and is no longer useful. The package directions states this fact. I do use DE around my yard and my barns for flea and tick control and it works great - only until it rains - I then have to reapply it.
I conducted experiments years ago with two groups of cattle using DE internally to control roundworms. The DE did nothing. The control group cattle would still have stools with roundworms that the DE did not harm.
When taken internally - it acts like a bentonite clay - it will bind together and produce more stools - BUT - sometimes it will aggrevate the intestines because it will coat them - much like grease coats kitchen sink drain pipes.
Too much DE can cause the intestines to stop up and become unable to produce a bowel movement. I am not disputing your results - I just want to warn other readers of this forum of the danger of internal DE use.