Overhead compartments are being massively overloaded by passengers trying to avoid the fee for checked baggage. Now, consider that airplanes are mostly older than this recent change in airline fees. They are designed to carry most of the baggage in the hold, underneath of the middle line of the aircraft. And when airlines check baggage into the hold, they weigh the bags at least once, and mark the overweight ones. Carry-on bags are almost never regulated nor controlled with regard to size and weight.
Consider the Hudson landing. It is probably fortunate for Captain Sullenberger that both engines failed. I really wonder - if only one engine had failed, if the centerline of the plane was below the weight distribution of the luggage, would the plane have flipped over?