Because if there is a front-end collision or a rear-end collision, the damages will be greater at those locations. The middle of the train is by far the safest for persons.
High-speed trains in Italy can reach speeds of up to 400 km/h (248 mph). The fastest Italian high-speed train reaching that speed is the modern Frecciarossa 1000, which connects the main cities, including Turin, Milan, Florence, Rome, Naples and Salerno.
This comes after recent incidents of fire reported in some trains. According to railway officials, the decision to restrict the use of the charging ports was taken as a precautionary measure.
That will be because they have limited power output and probably won't power a cleaner's vacuum or similar high power devices. I wouldn't take the laptop charger too seriously; it will undoubtedly work with other low power appliances too. My guess is that laptops require more power to function vs a cell phone device.