It used to be charging you to send packets through servers that they (in this case, Sony) own, but now that may or may not be the predominant use case in this era of games as a service where the developer needs to run the game through their own servers anyway. The reason Valve, Epic, and CD Projekt don’t charge you for it is because you’re paying for it every time you buy a game through their stores, which also used to be a less prominent situation on consoles, but now well more than half of games are bought digitally on consoles as well. So PC has taken more and more market share while consoles continue upping the price of their mandatory subscription fees for online play, and one day they’ll sit there scratching their heads, wondering where all of their customers went.