Bikes are perfect. If you need proof, notice that the essential design hasn't changed much since the addition of the chain. Two wheels, a triangle in the middle, another in the back, a chain and some gears to make it go.
Of course the materials have changed drastically. Steel is still available and has become quite fashionable with city bikes. Aluminum is a lightweight option and carbon has created the stiffest and most efficient frame. But outside of lighter, faster, stronger, the frame and design are timeless.
I think the design being so simple and so perfect, it creates a connection with the rider. Riding a road bike has become almost addictive. The speed that your legs can push you. The feeling of conquering a hill, beyond the obvious quad wrenching burn, and watching the miles add up.
Or of course it's just the endorphin rush and I need my fix.