Most normal coffee beans that you get in the supermarkets etc, or Italian style are dark roast, which is more bitter by default. In the UK most people prefer dark roast, it's what is most common and has even been marketed as strong and sophistcated.
On the other hand a medium roast natural process coffee is low bitterness, with almost a sweet and fruity complex flavour. So any bitterness is very obvious, as it simply shouldn't be there in the first place. This is the kind of coffee I make with my pourover.