I feel like since the Gamecube era, 3D platformers have been slowing dying off. Don't get me wrong, it's slowly coming back with Super Mario Odyssey, Hat In Time, ect but in recent years since the Wii era it has only seem like Mario has been the only one getting 3D platformers or at least great 3D platformers at that.
It's true. Halo 1 and GTA3 showed the industry at large that the real money was in those types of games. In fact, it led Microsoft to purge any platformer in 2004 like Psychonauts and Oddworld Stranger's Wrath from their portfolio, and is also why Rare justified Nuts N Bolts' existence. "Gamers just wanna shoot things!" is a quote I paraphrased from the 1st 15 minutes of Banjo-Kazooie Nuts N Bolts.
Of course, the success of Halo led to a lot of copycats which didn't reach the same highs... until Modern Warfare lit the world up like never before. From that point forward First Person Shooters were the go-to genre, and Call of Duty was the new king. With Activision pumping out constant entries and tons of developers making their own types of FPS games, every other genre died down while the FPS became the most popular.
Needless to say, platformers got hit hard. For the longest time everyone was trying to make the next Mario, but by the mid 2000s everyone wanted to take CoD's market. Platformers got scarce; Rayman and Donkey Kong went back to 2D, Crash burned out as soon as Naughty Dog left him, Spyro couldn't do anything without Insomniac Games, and games like Psychonauts and Oddworld Stranger's Wrath were lucky to even be sleeper hits. ND retired Jak and Daxter after 3 games and Sucker Punch did the same to Sly Cooper. Sonic kept making 3D platformers, but got so much wrong with some of the entries ('06) that he became a hideous laughing stock for years to come, getting mixed reception at best. There was also the idea that platformers are for kids and losers, and that Real Gamers played gritty mature shooters and the like.
For Platformers, there were honestly only 3 franchises that regularly made 3D entries.
Mario was never gonna die out; he basically carried the Wii and any main series game, like Sunshine or Galaxy or 3D Land/World got near unanimous praise.
Sonic also had a steady stream, but it was consistently bad and quite a broken mess with flaws that outweighed its positives.
Ratchet and Clank, the star of Sony's platformer trio was the only one born from its era that's still going with consistent quality. That's remarkable since that series was born and thrived in an era when GTA and Halo made games like that unprofitable. Their quality dipped occasionally, but R&C had quite a few hits on the PS2, PS3 and PS4, and that's even with Insomniac Games making their own FPS and other games. Super Mario, Sonic the Hedgehog and Ratchet & Clank were quite literally the only 3D platformers for a handful of years...with a cartoony aesthetic.
One thing people always say though, is that 3D platformers are returning, but they're missing something when they say that. 3D Platformers never really left, in fact some of the highest profile games of the PS3/XB360 and to a lesser extent PS4/XB1 are platformers. The
Uncharted series,
Assassin's Creed franchise and
InFAMOUS games are definitely platformers, the main difference is that they're not cartoony. They have the gritty look of their era and star a human, but if you've played enough platformers you'll see you do just as much running and jumping through obstacle courses as any cartoony platformer does. Those games come with a twist; Assassin's Creed is primarily stealth, but unlike Splinter Cell or Metal Gear Solid you're scaling buildings and hopping rooftops to get your prey. InFamous blends platformer with superhero genre, disguises shooter elements with Super Powers and takes some of the climbing from AC. Uncharted is just as much a platformer as it is a shooter and stealth game; if you're not navigating a vertical obstacle course, you're sneaking through enemy territory, and if you're doing neither of those then that's cuz you're currently in a shootout. Assassin's Creed and Uncharted especially were some of the most popular series of their era, and that's even with CoD dominating the market like never before. People tend to overlook them because they don't have the cartoony aesthetic of say, Gex or Banjo-Kazooie, but you're constantly jumping over and climbing over things in those games, and every platformer is about navigating obstacle courses for most of the game.
So yeah platformers took a big dive, but they made some remarkable entries throughout. Mario is his own level of quality, Sonic somehow stayed relevant despite a garbage record, Ratchet & Clank stood strong during a time when their kind was under attack, and Platformers as a whole changed with the times. Aesthetically Uncharted, Assassin's Creed and InFAMOUS are nothing like the cartoony ones, but on a gameplay basis they are no doubt platformers with a twist. Problem is not many acknowledge that, and these were some of the most high profile games of their time.