There are endless announcements of hub motor designs, and they all share the same problems:
Unspung weight is important to ride and handling. An electric motor of sufficient power (even for one wheel worth of propulsion) is heavy. The motor's weight can be minimized by operating it at high speed, but that means lots of gear reduction, which means a heavy, bulky, and expensive pile of mechanical hardware riding with the hub... increasing weight and packaging problems.
Electric-assist bikes and similar vehicles routinely don't even have suspension, negating this concern.
High power density leads to the need for cooling, which means hoses carrying liquid coolant between the motor and radiator. While many (probably most) DIY EV conversions make do with no more cooling than a fan on the motor shaft, continuous-duty motors in commercially produced electric vehicles are typically liquid-cooled. With a wheel motor, that means hoses running along the suspension links, flexing with suspension travel, and flexing through even greater angles with steering.
Electric-assist bikes and similar vehicles typically run only a few hundred watts, which is relatively easily dissipated through the surface area. This is a scaling issue - sometimes smaller is easier.
One reason to use a hub motor is to avoid the need for a jointed shaft to connect the hub to a motor or transmission... but those shafts are very effective and reliable, while a hub motor setup requires that the electric power cables flex with suspension and steering movement.
The cables for an electric-assist bike's hub motor are thin, minimizing the problem - this is the scaling issue again. Similarly, electrical cable to a wheel speed sender is not a problem, because the wires are thin.
Although most braking effort for an electrically-driven wheel should be regenerative action by the motor, a mechanical brake is still needed to supplement regenerative braking, as a backup, or for parking. That's difficult to package in the hub assembly with a motor (and likely gearing as well). I noticed that a recent design actually used a drum brake, because it was easier to package than a disk brake, even though drums have long been obsolete for automotive use other than for parking.