The OP doesn't really seem to understand what was going on.
First off, the NES was ULTRA popular. It literally brought home console gaming back to NA, after it almost "died" in 1983. In the interim, arcades were still super-popular, and home PCs were (very) slowly becoming more common. But the NES was the re-introduction/savior of home video game consoles in America. And Super Mario Bros. in particular, became a cultural phenomenon that surpasses "Pac-Mania" from the early 80s. Many games like SMB., Zelda, Metroid, etc., were genre-defining and innovative games, the likes of which people had not seen before. A LOT on NES in the 80s was new and fresh.
And you also have to take into consideration that the NES didn't really have any strong competition in NA either. While the Sega Master System had it's popularity in regions like Japan and Europe (and later South America), it never really got the penetration it needed in NA. Case in point, as a kid, I had never even HEARD of the Master System, nor seen it in stores in my area, until I read about it in EGM. Atari made a comeback of sorts, releasing new hardware, and re-releasing the 2600 model, their most popular. But it never truly challenged the NES either.
Then came the 16bit generation, heralded by the Turbo Graphx 16 in 1989. The Game Boy also came out in 89, opening up a new (true) portable gaming market. In short succession, the Sega Genesis came on the scene, and later the Game Gear as well. By the time the SNES finally launched in NA in 1991, all of those systems were on the market in NA. The SNES had far more competition, even from the NES and GB, than the NES had ever had to deal with. And while the SNES was super-powerful and stacked with awesome games, it also quite simply lacked that "wow" factor that NES had provided early on in the previous generation. And no, I'm not talking about a graphics "wow" factor, I'm talking about what I metioned previously: the fact that NES brought a lot that was fresh and new, as well as many (mostly) decent arcade ports, PC ports, etc. It was THE defacto game system of the mid-to-late 80s, and the only system that REALLY mattered (no offense at all meant to it's competition), within it's own generation.
Unlike NES, SNES actually had a battle on it's hands. And having people spending money on Genesis, GB and Game Gear, inevitably bit into sales a bit. Then you also have to consider that other consoles, such as the Jaguar, 3DO, Saturn, Playstation, etc. gradually came on the market as part of the NEXT gen (probably too early, if you ask me), from 1993-1995. And even just back to the Genesis, unlike the Master System, it actually gained popularity and traction in NA, with the help of games like Sonic the Hedgehog, Streets of Rage, etc.
But even with all that said, it's really a poorly realized misconception that SNES "did worse" than NES. Yes, if you're talking pure hardware sold numbers, it did. But considering the heightened level of competition, and the fact that the SNES was still alive and kicking and trying to compete with the generation that followed it (even the N64), well into 1997, before it was finally done? It did pretty well for itself, and is considered a success. Genesis got an earlier start in that gen, and an early foothold with the popularity of Sonic. But there really isn't any arguing that by 1994, Genesis was already dropping off, and SNES, with the help of games like A Link to the Past, Super Metroid, Donkey Kong Country, Mega Man X, Final Fantasy VI, etc., was still standing strong. The SNES won it's generation in the end, just in terms of longevity and pure software quality. That isn't to say Genesis didn't also have an awesome library. It absolutely did. But SNES, at least to me, and I think to many gamers, just had so much more going for it.
