OS inflexibity and lock-down, lack of ports, and heat dissipation for sustained CPU load are probably the big three. Low RAM and storage are also factors for ma

OS inflexibity and lock-down, lack of ports, and heat dissipation for sustained CPU load are probably the big three. Low RAM and storage are also factors for many desktop use cases. It's really cars vs trucks. A phone is a car. A desktop is a truck. A workstation is a big truck / semi. Convergence between niches tends to result in something that is good for neither, like a car/truck that can neither seat many passengers nor haul big loads.