Xfinity Stream blocks Screen Mirroring

My TV and cable has been down for 3 days because it was 5 days out to get a technician to my house and so I'm using Xfinity stream on my phone, I purchased a movie and once I start it and try to screen mirror it to my Samsung TV it then informs me it doesn't support screen mirroring. I would download the beta app on my TV but I still have no internet thanks too Xfinity making me wait 5 days for a technician. I can screen mirror absolutely anything and any app on my phone including the individual channel apps like AMC, can you explain to me why Xfinity who I pay $300 a month too has the access to screen mirror blocked???