Crash was huge during the PS1 days. Then Universal/Vivendi/Activision whored out the franchise with mediocre to terrible games until they just cancelled the whole series. Crash has four amazing games and like three to five passable, kinda fun, largely forgettable games. It also has like five or six absolutely shit games.
Basically, the publishers ruined his legacy. They did the exact same with Spyro. Banjo has two games that are well liked, those two game boy ones nobody remembers (but nobody seems to dislike), and an attempt to relaunch the franchise years later which failed, but is separate enough from the originals, due to the time between that had no Banjo games, that even casuals consider it a whole separate thing. Fans of Crash and Spyro know the Naughty Dog and Insomniac games are whole different series than the later things, but casuals don't realize that.
It's not simplistic gameplay, it's much more difficult and tightly designed obstacle courses. It's really an entirely different genre from Banjo, which isn't even really a platformer at all (almost none of the challenges involve platforming) but rather a collectathon, where the goal is to explore and collect shit to prove you explored. Crash is about doing tough platforming and getting all the crates was always an extra challenge. It's more comparable to Mario 64, but even that is like half true platformer and half collectathon. Crash is basically if you made an entire game of Mario 64's Bowser stages (which are the best stages). Spyro, meanwhile, is more like what Mario 64 actually is, with a heavy emphasis on collectathon stuff, and maybe more platforming than Banjo, but still not that much.
Also, Crash has pretty much the exact same personality as Sonic. Maybe with a bit more of comedic edge to him. And you talk about Banjo, but Banjo really has no personality. Maybe Kazooie does a bit, but not Banjo.
Crash is no more the same game three times than Banjo is the same game twice (and Conker is the same thing a third time but with swearing). Might as well say Sonic on the Genesis is the same game every time too.
To this day Crash is one of the only games with its type of level design, that being 2D platforming type levels translated to 3D. Other franchises tried to make it all about exploring when they moved to 3D, and that's fine too, but that types of tight obstacle courses that made up 2D platformers were never truly translated except for Crash and a couple of other games that have been mostly forgotten. Then years later Nintendo actually tried to do this with Super Mario 3D Land and World, because even they acknowledge Mario 64 and later games weren't the same type of thing as 2D Mario. Sonic tried to stay a little closer, I'd say that 3D Sonic owes a lot to Crash, but even then, Sonic Adventure 1's level design isn't even close to as good, and 2's level design is great and adds more speed than even Crash 3, but Sonic's gameplay is only 1/3 of the game.
Getting the Platinum Relics in N. Sane Trilogy really made me appreciate the level design in Crash 1. I used to think it had nothing on Crash 2 except the difficulty, but now I really appreciate just how finely tuned all the levels are. Everything fits together so perfectly to make for incredibly satisfying runs when you're going for those top times. All the lines and times and cycles line up so well. It reminds me of the best levels from games like Super Mario Bros. The Lost Levels or Ninja Gaiden, where, when you're playing well, the levels have a difficult but easy to recognize rhythm to them. I know I'm explaining it like shit but some people must know what I mean.