Every snuggle up on the couch with a blanket? A cape is just a handy, portable version of that. Before effective indoor heating, I imagine capes were a great alternative to binding heavy clothing.
What about obviously purely decorative capes? It’s just showing off. It’s hard to picture now, but there were times and places where being able to afford a non-functional length of fabric put you pretty high up on the social ladder.
I have experience with this in Northern Cameroon. Ladies could usually expect to get one 6 ft length of cloth to make their clothes for the year. Rather than styling that into two functional outfits, they’d choose to use the entire length to create one outfit with puffy sleeves, layers of ruffles and, as the topper, a huge long non-functional length of cloth tied around the waist just to show that they could. I imagine there was a time when capes served the same purpose.