It's time to put on my Star Wars fanatic hat. They aren't meant for troop transport. Think of them more like tanks. They're meant for ground assault. They were used in Empire to take out the shield generator so the troops could be brought in by ship.
BTW, it's still cold outside.
While I agree with your assessment of the AT-AT (All Terrain Armored Transport) the Empire had a questionable ground assault capability.
Goddam teddy bears beat them with sticks and logs during jungle fighting. Not even nimble teddy bears.