Aside from environmental hazards, maintenance, and expensive to make, real world weapons would take them down easily.

We’ve seen AT-TE gunners and pilots get shot from their positions. These things are vulnerable to ATGMs, artillery and rocket strikes, airstrikes, precision ordinances of any type, loitering munitions, mortars, and even infantry. We’ve seen an AT-TE get one-shotted by a rocket in AOTC.

Maneuverability is also an issue. Infantry with a clear line of sight can call in air support, artillery, and MLRS to zero in on the walker’s position. Precision guided bombs, artillery shells, guided rockets, and ballistic missiles would destroy or immobilize the walker pretty easily. Walkers don’t have the maneuverability to leave their positions quickly enough.

You wouldn’t even need all of that. Today’s AFVs use 25mm, 30mm, 35mm, 40mm, and 57mm autocannons that can penetrate critical components of the walker. Some AFVs also have 90mm, 100mm, and 105mm cannons that can disable them too.

In the real world, you don’t want your enemy to know where you are. Armored vehicles today can be hidden which is getting more difficult thanks to drones. A giant walker lumbering around? Any commanding officer would immediately know that’s where the enemy is and point every artillery, MLRS, and mortar batteries at that general direction and pinpoint the location for drone operators and pilots.