This might be social stigma, we will be stigmatized by society if we dont have appropriate clothes for right situations as such, we buy so many clothes that are visible depending on the number of occasions and everything because we have to look appropriate for that and this is where number of brands can stem up from too and this brand has brand value, because oh, you got that X company shirt nice.

Nobody cares what brand your underwear is because its hidden.

Such products are usually fewer brands because what matters is a huge chain supply. You most likely buy it if its available retail or not, you don't go look at an ad and say, wow I want that brand but the idea is to make familiar with it.

But even if you aren't. There are just so few brands with supply chain directly to retails that such things usually end up getting centralized and convenience of buying is the largest factor. You want to drive less to get this stuff whereas you might go far away just to get a nice pair of shirt and jeans for example something which, again has to do with the visibility of the product/social stigma

Technically, the supply chain thing also directs itself to products like cole drinks for example. You are probably drinking coke/pepsi because its available everywhere and usually the choice that you see in different drinks is just some permutation of a drink/brand which is owned by the parent company (coke/pepsi). The amounts of brands owned by pepsi/coca cola are quite a lot to be honest.