"pretty quickly" is a few years, not one month. Chrome dominated the browser market pretty quickly even though the richer bigger company microsoft already had most of the browser marketshare, and that was 3 years. Before those 3 years it seemed like nobody would be able to make a dent in microsofts monopoly, and then it was gone in just 3 years.

If steams fumbles as hard as microsoft did with internet explorer they too could be mostly gone in 3 years, replaced by a giant competitors product.