why are the bars bending with such light weight?
The bar in the first pic is bent from years of having heavy weights left on it, it took a perma set. It was more common when you had narrow benches, allowing for more droop on the ends of the bar. You'll sometimes see it if a bar is dropped across a bench too, but that is less common. Usually when this happened, the bars became a makeshift cambered bar for squatting. When they are bent like that, it allows for longer hand placement which some squatters like.
The second pic is Pisarenko, who in addition to having an awesome stache, was one of the closest men to a #600 Clean and Jerk -
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In that case, the bar is showing a somewhat extreme bend in relation to weight because it's being done on a proper weightlifting bar, than say a general purpose or powerlifting bar. They are generally left more springy than the latter two.