Short answer is because we don't have their permission to do so. What we are able to do though is link to Cargurus results matching your search. So if you run a search on AutoTempest, you'll find a link in the 'Comparison' section of the results page to Cargurus (along with several other sites), and if you click that, you'll get their results for the same search, without having to enter anything again. That way we hope to make it convenient to get results from everywhere, even the ones that we're not able to show right on our page.