Indies don't have to sell consoles and are generally less ambitious. Nintnedo got their mascot know how from mimicking Disney and similarly sony for Pixar. I believe nintnedo used to sell Disney themes cards and Sony has stated before that they wanted to make Pixar like story driven games in an old documentary explaining their close relationship with insomniac studios.

Owl Boy and Ori are some of the best games iv played and they have iconic characters. I believe Indies make better mascots than most AAA studios.

To make a good mascot a dev team needs talents and skills different from mere programming skills or creative ones, but aimed at the game concept. Arts, marketing and human communications, and maybe even psychology skills are needed, a few times game devs have them too, but it's not common, so medium and large dev teams can usually afford these additional people too, small and indie teams must count on what they have.
Every now and then it can happen that small devs too create huge games, and sometimes even with iconic mascots, see Minecraft, one of whose baddies, the creeper, cited by OdinHades in the first comments, has become quite iconic.