In the US most mobile carries will hijack your traffic, either slow it down(they call it whatever saver), or replace the data with their cache.
I tried a T-Mobile MVNO or T-Mobile(?) phone a few years ago, noticed regardless whatever resolution I set inside the Youtube app, it is super blur on Cellular but it works fine on Wi-Fi. The I found that the carrier setup its own cache of low resolution youtube videos, it will hijack all your requests to youtube and replacing the content to its own cache (360p videos).
That's how they give you "unlimited" data as you will never able to use it.
I tried a T-Mobile MVNO or T-Mobile(?) phone a few years ago, noticed regardless whatever resolution I set inside the Youtube app, it is super blur on Cellular but it works fine on Wi-Fi. The I found that the carrier setup its own cache of low resolution youtube videos, it will hijack all your requests to youtube and replacing the content to its own cache (360p videos).
That's how they give you "unlimited" data as you will never able to use it.