On cell networks, video content is by far the largest consumer of bandwidth. And the default for video generally is to auto-adjust the resolution to the highes

On cell networks, video content is by far the largest consumer of bandwidth. And the default for video generally is to auto-adjust the resolution to the highest quality that the network supports. This kind of sucks, since bandwidth is a shared resource for all users of a given antenna on a cell tower. Though Speedtest on your cell might show your connection speed as 100 megabits/sec down, cell networks special-case video by identifying it as video and rate-limiting it to something like 1 megabit/sec. This is considered "efficient network management". For T-Mobile, this based on the plan (https://www.t-mobile.com/cell-phone-plans https://www.t-mobile.com/cell-phone-plans), they sell either "SD streaming" or "4k UHD streaming". "SD streaming" is a fancy way to express that they rate-limit identified video streams to 1 megabit/sec. They identify video streams by watching the IP your phone is connecting to and/or the hostname mentioned in the TLS SNI header and checking if it is Youtube, Netflix, etc. Sending video content over a VPN removes their ability to understand what the content is.