I recently discovered that T-Mobile does this too, but they actually let you disable it on their site. Ostensibly, it's a feature for your benefit (somehow), and they're doing you a favor by enabling it by default. In reality, of course, it's for their own benefit, and they're banking on people not realizing it can be disabled. I suppose giving you the option lets them advertise things like "no throttling" and "4K streaming supported" while still reaping the benefits of throttling/lower-bitrate streaming.