When you shop for clothing, you don’t care about whether a particular garment fits a range of body shapes and sizes. You only care that it fits YOU.
I’m not saying you are selfish, just that we each look for clothes to buy that fit our exact needs and wishes. We get excited when we find something that is just what we were looking for. One of the highest compliments we give an article of clothing is to say “it is like it was made just for me!”. Your customers are like this too.
Brands, on the other hand, usually think about how to fit many people, not how to be the perfect fit for one person. Unless you are truly a bespoke brand, you have to sell to more than one customer to be profitable. This mindset can be taken too far, though, to the detriment of your brand.
If you are trying to fit everyone, your fit will never be perfect for anyone. If you aim for enough specificity to elicit an enthusiastic “it was made for me” reaction, you’ll get it from those perfect-fit customers and fit another group of customers decently well too. If you aim too genetically with your fit, you run the risk of being unremarkably so-so and stand out to no one.