There IS a huge selection out there - once people have identified their style they go and buy the pieces that work for them.
It is not difficult.
Let's say a woman has determined she's a Katherine Hepburn kinda gal. Crisp blouses, wide-legged pants, narrowly pleated skirts with narrow belts., cardigans, trim jackets, nothing highly ornamented. Off she goes to various stores/designers to put together the right pieces.
Another person may have more of a shift dress/cardigan style. Regardless of season, shift dresses and cardigans can be found.
It works the same way for men as for women. My late uncle determined that he was an ascot kind of guy when he wasn't at work (and sometimes at work also), so he wore shirts that accommodated ascots. He often wore vests instead of jackets. He knew his style and worked it for decades.