Why aren’t there more tricycles with rear disk brakes (between the two rear wheels) Just curious if anyone has seen these before, it would be a rare bird.  I'm looking for a trike where the mount for the rear disk brake is mid-axle between the two rear wheels.  What are the technical or marketing reasons these aren’t these more common?

My friend's trike has some terrible hub/band-brake on the rear axle.  I put on on a front 180mm disk brake, that helped immensely, but I'm very curious about a rear disk brake too.  A fully loaded trike plus the unloaded weight of a trike can be quite significant.  [NB:  looking for a non e-bike trike]
Check out the Atomic Zombie plans for "deltawolf"    These are do-it-yourself plans, they don't sell completed bikes.

Here's someone's bike from the rear



There's nothing to stop you putting the caliper mount further out for a 180 or 203mm rotor.  You could also set up the same on the left-hand axle.

Note this design is a single driven wheel rather than a solid axle or a differential.

Someone's build: http://atomic-zombie-extreme-machines.blogspot.com/2010/08/building-deltawolf-recumbent-speed.html