My Jeep Rubicon is a 6-speed manual. IMHO, a manual is much better for navigating extreme terrain than an automatic. Yes, Hummers and Abrams are all automatic transmissions, and handle rough terrain well enough, but I prefer the added control and ability to manage where and how my torque is getting used.
4wd and manual transmissions to me are the natural match.
Abrams tanks are fun to bounce around in, I did some in NG and I wouldn’t want to imagine manually shifting gears on it.