2011 Moto Guzzi Stelvio NTX

[Travman]

I wonder why all these bikes use the spoke wheels? I don't see the benefit.

are they significantly stronger than cast or forged?

All dirt bikes use spoke wheels.  These adventure bikes have off-road aspirations therefore the more off-roady the manufacturers want their bike to be the more likely they will use spoked wheels.  Spoked wheels are strong and they are flexible too which is important when hitting a lot of bumps & rocks.  Even if they do get damaged they can be repaired.