Yes, they have. The front-facing camera in my Surface Book is of a much higher standard than most -- better than most separate webcams in my experience!

As you've found, though, I suspect that this is something which is mainly available in 2in1 devices. I suspect this is because the screen (or "clipboard") can be much thicker than is considered "sexy" or "acceptable" in traditional laptops. With thickness more akin to a phone, a camera module more akin to a phone's can be installed. I suspect that most laptop vendors aren't willing to trade screen thickness for webcam quality.