Many publishers are attempting to get PC developers to cap their PC games at 30FPS because they don't want PC masterrace taking over their peasent consoles.
In some cases it's also the console manufacturers paying for games to be made exclusive, or for PC ports to be delayed in order to squeeze the sales on the consoles for the unwitting public.
Publishers aren't all necessarily asking for their PC Ports to be capped at 30FPS, rather they're not giving enough time for PC ports (feels like an oxymoron) to be optimised and so the developers have to try and stick as close as they can to the console version quality.