Testcafe uses testcafe-browser-tools to find installed browsers.
On Windows the registry ("reg query") is queried. This does not work if registry access is no permitted without administrator privileges (company policy). Since browsers can be found via PATH variable Testcafe should attempt to locate browsers via PATH variable as well. I know that the browser path can be passed to testcafe but it should not be neccessary! If the PATH variable would be used the command "testcafe --list-browsers" would work as well on those Windows machines.