Forrest combat's not very conducive to ANY vehicle combat though, which is a real thing to consider with the AT-ST's. An M1 Abrahams in a forrest is at a distinct disadvantage to both traps and human assault as well as attack from other tanks (who would be at equal disadvantage).
I think what we need to ask about the AT-ST is that, if we don't accept the obvious "Lucas didn't think them out much and just wanted them for eye-candy to to explode", then we have to see if there's some explanation for their seeming ease of destruction...
For fire from other combat vehicles of equal power, we only have a brief moment of Chewie firing on a single AT-ST. WE could argue that he has let a couple shots loose before we actually have the camera cut to that moment, as the AT-ST was seemingly stopped for no reason that he was shooting at. Perhaps it had stopped to turn and see who was shooting it? It's plausible... Odd, but it makes an excuse. With that in mind then, we could assume the AT-ST had taken a few shots to its rear portion already, combined with those which it had already taken and any possible damage inflicted by Ewok weapons (perhaps a boulder smacked it in the rear portion?).
Then, if we go by the idea that the AT-ST is slightly weaker in the rear of the command pod, as most armor vehicles are a tad weaker in the rear (Such as the Tiger I from WW2, which required a pretty point-blank and direct hit on its rear to be destroyed by most allied tanks). Chewie blasts the AT-ST he clears out by shots to the rear, so we could assume there's a combination of pre-weakened "hits" there by whatever... A few possible shots Chewie gets in on it from a greater distance that we "miss" or are just off-screen... And last, the idea that AT-ST's have a combination of possibly their energy cell compartments in the rear with a slightly weaker armor point. These things could add up to Chewie's AT-ST being destroyed easily enough.
For the walkers destroyed by the Ewok traps, there's a couple... The hardest to explain is the walker on the wobbly log trap, as that thing seemed to be the Ford Pinto of Star Wars as it just blew to pieces on impact with the ground.
My explanation of the tripping walker would then be that it sustained damage previously... Small arms fire, boulders, or even an Ewok mounting it and pulling and ripping at anything he could, possibly even exposing a fuel-port perhaps? Or maybe even a Rebel collaboration with an Ewok to plant a bomb on it so when it fell it detonated it and caused the most possible damage? There's some possible excuses... Far-fetched or ones that maybe don't seem practical for the situation, but sometimes unpractical events occur in combat that make you scratch your head later too, so it's possible.
For the Log Smash, and for the cutscene one of a single chopped tree collapsing on a walker and crushing it, I believe these to be "reasonable" situations without extra explanation personally. The logs that smashed the command pod of the one AT-ST were roughly the diameter of the pod itself... I think if two logs forcefully came together on a modern US tank, which is a fair bit wider than an AT-ST command pod, then it is reasonable to think they'd do some serious damage to the tank's armor or even be capable of knocking the turret off? It's tough to say without really accurately knowing the weight of the logs, the height they were raised, and such... Technical junk, but just by watching it, it looked reasonable.
I'd say the same for the cutscene of the chopped tree falling straight down on a Walker too, and even moreso because it lit squarely on the top of the AT-ST it destroyed which would put tremendous pressure on the small legs of the Walker and most likely crush the joints of the walker as is what seemed to happen in this Walker's demise scene. Resulting damage for its power supply (star wars vehicles, at least fighters, seem to run off of a fuel so it's reasonable ot think it's possibly combustable and that similar stuff's used on walkers and such) then means explosions all around...
The AT-ST isn't big either, and as a "Scout" as opposed to being referred to as some form of heavy assault-type walker, so its armor likely matches.
I'd say, short of running AT-PT's (a pretty common walker-type from EU we mostly all know), the AT-ST is nimble, heavier armored (than an AT-PT anyway), can handle the valleys and hills/inclines of Endor, and is a simple infantry support vehicle.
The LAV is pretty easily slapped around if it gets caught in a heavy combat situation of any kind (even just infantry), so maybe the AT-ST's simialr to it, without the troop capacity since it could carry 4 or 5 guys at most, counting the crew.
The AT-ST then seems a reasonable choice for Endor. That and infantry. The speederbikes were more cnfusing to me, but I can see their reasoning behind their use, and of course AT-PT's WOULD have been cool to see but are just EU stuff so they ain't there.
I'd say any # of walkers were NEAR the main generator though too... This is a remote area, from what I can gather in the films, but the area surrounding the actual generator itself (where they expected the attack) appears possibly miles (as in hundreds or more even) away from that rear bunker area. That area may have had a pre-fab garrison, landing platform(s), and of course the heavier walkers like the AT-AT's, or other vehicles even. Something expecting a bigger force than a shuttle's worth of Commandoes anyway.