>>86786 (OP)
Tanks aren't as all terrain as you'd think. They impart a consistent force on the ground when they move, and when ground conditions reject that force you're fucked. Even in the modern era of information and satellites a tank operation can be foiled by an area of slippery flat stones stacked near the surface by some geological process or any equivelant ground feature. There are obvious limits to traversal and man's attempts to bring more metal faster to places it shouldn't be has led to the development of machines which are pretty much giant robots already. Ground pressure issues from bipedal machines are grossly overstated and the power of the arms on construction vehicles for instance are grossly underestimated by popular realism -just look up some videos of people loading backhoes into trailers using only the backhoe's arm, or other tricks demonstrating even large vehicles lifting their own weight.
The military will burn money just for a piece of equipment that functions as intended, because that's what allows force multiplication at all. Truck gets stuck in a ditch, infantry don't arrive, cannons can't target in the stormy sea -that's what causes history's military facepalms. So tell a general, "That gun you like because you know it works? Our policy of putting that shit on everything has resulted putting it on legs." and he's happy because now he can drive his favorite gun straight up a cliff where only mountain goats would dare. I think people consider legs as being wasted weight or excess, but a better viewpoint might be to see the legs as a seperate piece of standalone equipment.
For the awesome and almost practical stuff consider that a fighter jet needs to be in a high energy state to dodge a missile, but something like an armored core would realistically be able to dodge by juking one way and ground-braking the other way just like in the game. Mission kills are a serious problem for military vehicles, since a straightforward approach of adding armor can prove insufficient to keep a tank in the fight. Legs might have better survivability since only one leg is needed to move, even if it has to scoot across the ground. You could take advantage of that and armor the legs in a way to keep one working and the other from collapsing when damaged. Having arms is effective for switching weapons and equipment which could help an old platform stay relevant. In WWII most tanks that stuck around for a few years ended up with so much stuff bolted on they were pushing the limits of what the original vehicle wasn't designed for. Modern vehicles are static only because they aren't fighting serious wars, and they'd age like milk if they did. Even the largest battleship in existance was designed with a weapon swap in mind in the face of expected escalation. And being able to freely target a weapon is an obvious development for any vehicle, so fighter jets are starting to mount their missiles on arms instead of the wing to fire freely in any direction. A giant robot could stick their arm over a hill or around a building to shoot without endangering the body wheras tanks require luck or preperation to do the same -surely that boost to survivability is worth balancing against. Robots have the advantage of rocking back while firing by collapsing their frame, or assuming a more geometrically stable firing stance, while tanks have issues firing a cannon too large for their weight class, especially if they want to make rapid follow-up shots.
Finally realize cost is a matter of time. Tanks are cheap because humans chose to make lots of tanks, and they started on that because they had trucks. If robotics becomes a more significant part of civilian life those components will inevitably approach dirt-cheapness, and the military will use them. Metal is metal, industrial base is industrial base.