system
Given the following post, respond as if you're commenting on Reddit:
human
[Starwars] Why are the Imperial walkers so high off the ground? It just seems like a huge wast of space, and makes them unstable. And vulnerable to things like what happened on Hoth...
gpt
The Galactic Empire is not fighting a war for survival, they are quelling a resistance and keeping the peace. Given that they also have insanely huge production capabilities it makes sense that they would shift design towards intimidation rather than outright efficiency.

There is a lot of propaganda about the AT-ATs high stature about helping with landmine resistance, which while true likely does not provide much help against conventional arms by producing such a prominent target. As a result it had to don massive amounts of armor which while effective has severely slowed its speed on the battlefield.

The events on Hoth were somewhat unprecedented. The rebel forces had a highly effective shield generator that prevented orbital bombardment and as a consequence the imperial troops did not have air support. The rebel's speeders were found to be capable of entangling the legs of the walkers which was a brilliant exploitation of the walkers' design, however even without Imperial air support it was a very dangerous tactic. 

This is actually rather similar to contemporary armored vehicles. A tank which may be fearsome on the battlefield will be destroyed by simple molotov cocktails, tracks can be blown off by improvised weaponry, optics blinded by paint bombs etc. However these tactics all require extreme close quarters engagement, much like the speeders' tow cable attacks, and the approach to the target is the hardest part. I'd assume the Empire simply didn't imagine enemy troops getting close enough to the AT ATs to exploit any weaknesses.

In TESB, it was pointed out that Admiral Ozzel came into the Hoth system too close and by doing so alerted the Rebel Alliance to the Imperial presence. As a result their planetary shield system was engaged. It is clear then that the Empire was not anticipating that shield to be up, and through a fluke they were denied air support in their assault.