Yeti has become a "lifestyle" brand. Early on, offshore fisher folk used the coolers to store their ice for icing down their catch, for many days on their offshore fishing excursions. They're very, VERY expensive coolers, so it became a sign of "prestige" amongst these fisher folk to own one of these expensive Yeti coolers, and wear clothing branded as such. Not unlike the "Salt Life" brand of apparel, or the "Costa" brand of sunglasses and apparel. It's basically for wealthy rednecks to show off to one another, or to show up less wealthy rednecks, or something.
Yeti is an Austin-based company, so the brand is also popular amongst those who like to push the "wear local" type of lifestyle.
I do not own any Yeti apparel or any Yeti coolers, but I do own a 20 oz Yeti vacuum-sealed steel cup, which does a nice job of keeping beer cold for FAR longer than I'd ever want or need it to stay cold.