Part of what you're sensing is simply a function of how our brains experience speed. At low speeds, it takes more steering or lean inputs to make your bike change direction than at high speed, relative to time. At highway speeds, every second you're moving twice as far as you do around town in a second, but your brain is still processing at the same speed it does while you're walking around at 3 mph. The relative greater distance that the front end changes direction in constant time compared to low speed, with the same steering or lean input, makes your brain think it's "lighter." It isn't. Things are just happening faster.