Gravel bikes have an upright geometry with more rider weight distributed through the seat, so that is why you see this bias towards rear suspension. Personally, I think I prefer no suspension system at all, but my rides aren't very bumpy.
Cannondale's "Kinpin" system seems like a combo of Giant's extremely dropped seat stays and Trek's IsoSpeed decoupler (though I'm sure Trek would take issue with this characterization and provide pages of documentation about whey their system is more advanced).