>>96287643
A multitude of pseudo realistic reasons and story bullshit.
Pseudo realistic:
>Cheap layered point defense saturates every area on the modern battlefield. Aircraft can't loiter and standoff ammunition struggles to get good terminal guidance in the ECM
>Sensor denial is the new default in war. It's near impossible to target any precision guided munition past a few kilometers
>Armour is in a state were it typically beats the common warhead but they under-perform against ugly shot angles and modern melee weapons that a mecha can bring to the field
>Countermeasures are functional at a human-scale, omnidirectional APS can defeat most incoming shots. A mecha can keep its aps facing the threat while moving, shooting in different directions and picking angles dynamically making it more efficient on the field than traditional vehicles.
>Mechas have weird silhouettes, can crouch, go prone, hunch and more making them hard to identify for modern fire control
Pure fiction:
>Elite pilots with neural links vastly outperform traditional vehicle crews. The human motor-cortex only properly maps to bipedal torsos with arms, hands and a head. Everything else causes blackout and lag.
>Cognitive firewalls are necessary to resists memetic cognitive jammers that will simply make you pass out the moment you enter a battlefield. These firewalls need a sense of self and key off against the human silhouette to work, everyone in a tank gets his brain turned into mush.
>The metamaterials used for modern armour require articulated shapes. Inertia dampeners need separated masses in humanlike posture to stop impacts. Cooling relies on special gel-mixtures that require artificial muscles to pump coolant like blood. Phase-tech requires alternating grounded and ungrounded contacts (feets, legs) to bleed momentum. Reactive armour gel needs to channel plasma across fold lines that are easier to create on human limbs. The electromagnetic armour fields align along limb vectors etc.
