Because Sony has been building the "Playstation" brand image in literally all around the world, while the other 2 didn't.
Xbox only popular in the North America and some parts of Europe, and it's practically non-existent outside those territories.
Nintendo was pretty well-known, but they chose not to expand their market outside Europe, North America, and Japan, which resulted in a drop in their brand.
Sony has been expanding to lots territories on the planet, even to places that were never considered as a "market potential" by all of its competitor, like South America, Middle-East, and Asia. The result was Sony completely dominated the market, and bring more sales to their console (almost 1/3 of the PS4 total sales were coming from those countries).