Why is the video quality of Xfinity Stream on demand videos TERRIBLE?

As much as this Xfinity cable and internet service costs... ($300+ a month!) you think we could stream in 1080p or even 4k and have the resolution of the screen be beautiful. Its always terrible quality with blotchy squares whenever we stream on Xfinity Stream! This is unacceptable service and we shouldn't have to pay an arm and a leg for it. You all say you care so much, fix it? Many people are complaining about it. I have all the correct hardware and every other service besides Xfinity works perfectly. It literally feels like robbery every month when I go to pay my Xfinity bill. It seems like after this months bill I am going to get a different cable provider, especially if Xfinity has no drive to fix their quality issues.