It's not just the filtering. It is also that many datasets are full of errors. I wrote a data analytics tool that I would test out on a bunch of open data sets like this one. One of my favorites was the Chicago crime data. The tool could quickly find (and fix) a bunch of errors. I tried contacting the people who published the crime data and even offered to show them how to use my free tool to clean up the data. They could not have cared less that their data set had large numbers of errors in it.