Playstation was successful for three key reasons:
1. Pricing competitiveness. When Sega Saturn announced their price of $399, Playstation undercut them by selling it at $299 (despite them initially planning for a $399 launch). Before Nintendo entered the scene they dropped the price again to $199. The cost of games was also very minimal. Many games cost $40-$50 new. Some even cost $30, and prices dropped more significantly. Meanwhile, N64 game prices were at least $60 and some as high as $80 or $90. Playstation was cheap for all consumers.
2. Ease for developers. Not only was the Playstation hardware easier to develop for than both the N64 and Saturn, but Playstation had little restriction for publishers on their console. This was much different than years previous where Nintendo had very high restrictions and limited/censored content for audiences.
3. Marketing. Playstation was a marketing beast. There were many different slogans, mascots, etc. The image was both kid friendly and "mature". They were edgy and casual, it was a perfect balance. Hundreds of millions went into marketing the Playstation. In just the UK a hundred thousand was used just in impromptu marketing each year...that's in one small region for specific marketing...every year. I don't have data for the entirety of the Playstation era, but I'd be willing to bet it was upwards of $500 million dollars on the very low end.