guns

even other than bridges heavy tanks have to be much more selective when planning routes, light armored cars and smaller tanks can more or less go in a straight line where heavy vehicles have to avoid certain types of terrain (slopes, mud, narrow passes, etc.) to a greater degree, and take a longer, more circuitous route.

the T-80,90, etc. have less vertical cannon traversal than the abrams as well, this is due to differences in combat doctrine: america/the west expected a defensive war in the cold war times, while russia expected to be on the offense. therefore western vehicles are large, heavy, reliant on stable and secure logistics situations, and designed to fight often from prepared defensive positions, with long range weapon systems and optics to use them accurately, whereas russian vehicles are smaller, cheaper, lighter, more mobile, easier to maintain, with shorter range but versatile weapons (one of the T-series of tanks can launch AT missiles out of its smoothbore cannon IIRC), because they expected to be on the move and their combat doctrine emphasized closing with the enemy to negate optics/range/sensors advantages, they built tanks to be able to use railway cars and roads and maneuver more easily in tight terrain to attack from unexpected directions and outmaneuver defenses.