What about Spyro? What about all the other maskot games? If you're asking why Spyro isn't as popular as he was a decade ago, it's because there hasn't been a proper Spyro game for quite some time. Nintendo, on the other hand, makes several Mario games a year and has been doing so for the past 3 decades. This increases mindshare and all that stuff. See Call of Duty, Battlefield, FIFA, Madden, etc. Same with Pokemon-- it too is an annual franchise. Nintendo games aren't special. If you make a game every year (or in Mario's case a ton of games every year) you're audience will grow.
Nintendo just makes a ton of games for their franchises over a small period of time. See what happens when they release the next StarFox or Icelimbers or whatever franchise doesn't get a annual/semiannual release.
Look at this list of Mario games releases:http://en.wikipedia.org/wiki/List_of_video_games_featuring_Mario
