I suspect this is a workaround for 1x drivetrains. 1x drivetrains require absolutely massive cassettes to get a useful gear range. With 1x being a trend and cas

I suspect this is a workaround for 1x drivetrains. 1x drivetrains require absolutely massive cassettes to get a useful gear range. With 1x being a trend and cassettes being a very visible component, huge cogs have become super fashionable for now. Derailleurs are a limitation, because the whole assembly needs more length to get around those enormous cogs, plus the long jockey lever arm to accomodate the full slack range of the drivetrain. The whole assembly eventually gets pushed further down where the chain and fragile jockey arm are exposed to the bits of nature they can snag on. Splitting the jockey arm over a third jockey wheel like this avoids that problem. So this design might allow even huger cogs.