Could be the tire compound and the tire has stiff sidewalls. The only thing I can think of to make it smoother is maybe aftermarket coils with dampening adjustments or possibly air ride ? Very expensive alternative for a smooth ride though.
I find the tires way to smooth because of the soft sidewall... The tires are only passenger all season so they are one of the weakest in side wall stiffness. If you think they are hard do not drive on grand touring or higher!