I've heard that, but have seen no official source for it. A corporate critter at one of the release events said it was about costs.
Toyota brings back the solar panel on the Plug-In Prius Prime – but now it powers the car | Electrek The automaker plans to bring it to America, but the reinforced glass sheeting currently used for the solar panel is not passing the US rollover crash tests. They are reportedly working on a solution, but there’s no timeline for a US debut.