Because the facts don't support it. There are a number of app-based minicab services that are able to comply with TfL regulations. Uber here is failing an extraordinarly low bar - report serious crimes when your drivers commit them, do not implement a system to decieve regulators. The regulators are not coming down Uber-like apps in general, or on some theoretical - they are coming down on Uber in particular for its history of action, with evidence-backed specifics.