Because they are? 4WD is another name for 4x4, which is more for off-road applications, with a locked (or lockable) center diff and usually a rangebox, while AWD is for sporty vehicles with either electronically controlled or open center diff, it's much more modern. To put it simply, 4WD is designed for max traction, while AWD is for max drivability. Usually it means the same but the difference comes in the type of terrain. For example AWD will perform better on ice and 4WD better in snow. At leas this is how I understand it.
Although you won't have any model for the drivetrain components (no transmission or halfshafts). If you want to keep the looks, you can use the CJD Special Tunes mod, wich ads AWD and RWD transfercases for both the Covet and the New pessima --- Post updated --- I'd say that a 4WD system allows the disconnection of one of the axles, while AWD systems are permanent. For example, systems with any type of center diff (open, Limited Slip or lockable) or a viscous coupling (since it always send power to the other axle on slipping), are AWD. Systems with connections like a clutched splitshaft or a 2H-4H transfer case, are 4WD. So, an AWD system doesn't need a command to engage the system, since it is always engaged, on the other hand, 4WD systems require a the command to engage the undriven axle (either by the driver or the computer).
Because nowadays AWD and 4WD have evolved so much that they are almost the same and nobody can tell the difference anymore lol, back when AWD came out I imagine it was a huge thing and everyone knew the difference
