Really the simplest answer, and most obvious. That said, I would never discount the work that Sony's leadership did, in Japan, in the United States, Canada, and Europe. They went directly to a multitude of developers with support, both technical and monetary. They provided a platform which publishers could rely on for being successful. Kalinske did many of these things with SEGA, and Nintendo did them for years as well. Sony just did more of it, and had more to work with. They had one vision and no one got out of line. Perfectly executed business plan.
That said, most "gamers" chose the N64 or Saturn instead but PS1 bagged the ordinary consumer.