For me-- the times when I get to play-- half the fun of character creation is finding something cool within the traits and assumptions of the setting within which to base my character around. If a setting only has certain classes, species, backgrounds etc... for me the juice comes from creating within those barriers rather than wanting/expecting complete freedom. Because oftentimes that complete freedom produces less interesting results. Restrictions often mean you can't just take the top surface level ideas but have to start digging further down, producing more creative and interesting things and combinations.It means the world you live in exists before you do, so you are shaped by its traits and to some degree by its assumptions.