Human beings have a narrow, 15-degree arc of vision, that directs their focus. Outside this arc, the eye's ability to resolve colour and shape drastically diminishes. In fact, at the edges of vision, humans are effectively colourblind. The only visual signs that humans can resolve effectively across all directions are animations, especially tracking animations where objects enter the visual field, travel and leave it. But these are so powerful, users have trouble progressing any further than spotting the animated element - no matter what copy you write underneath. This makes it hard for visual elements to garner attention in this space.
But the real question is: is this really a bad thing? Sidebars and right-hand content are typically used for secondary content, and that allows users to employ a handy heuristic to avoid right-hand content in high-strain tasks. Humans have a narrow field of vision because they're bad at multitasking, and that's not something any kind of content is going to fix.
I wouldn't recommend swapping left-hand content with right-hand sidebars, either. I have seen a multi-variant test where a site put a secondary 'request a quote' form in left-hand space. It didn't turn out well. Lots of users converted and submitted the form, but phone surveys conducted afterwards indicated that nearly all the users had no intention of actually requesting any kind of quote. The quote form was positioned as though it were another step in the 'primary' workflow; users presumably completed it because they assumed it was necessary, not because they engaged with the content.
