Sure, it's easy to throw together 2 separate drivetrains on a bike and say you got "AWD" but everyone who's done it knows it doesn't work as well as you think it might. The different rates of acceleration, even if both drivetrains are "identical", make it inherently unstable (see Hurst Hairy Olds or Mosler TwinStar) with a bike, exacerbated on slippery surfaces. True AWD is a single motor turning all wheels. The Christini AWD system does this (with pros and cons ofc), and on newer ones it can even be switched off so just rear wheel is powered.