You're given a fairly good set of protections in the Tor network: three layers of encrypted misdirection, plus a browser that blocks many tracking features. Using a service like Tor 2 Web or Onion Cab not only removes the browser-based protections, but also lets anyone listening to the network (or the proxy server admin) see what pages you're connecting to. The point of Tor is that users can connect without being eavesdropped on, and going through the clearnet, even with https, seriously cripples the efforts made to protect users.