It's baffling to me that the Crash licence has been so misused for so long (when it wasn't simply left sitting around).
No shit the collection is selling. We can harp on as much as we like about how Super Mario 64 revolutionized everything and and OMG analog controls and it sold better yadda yadda yadda, but at the end of the day, the Crash Bandicoot series has the triple distinction of:
- being a more accessible take on 3D platforming than SM64, not to mention being technically more faithful to the essence of 2D platforming (SM64 evolved the formula towards sandbox and exploration and lost a bit of the straightforwardness and immediacy of the 2D Mario)
- selling consistently well over the first 3 episodes, with no real decline (6 million units for CB1, 5 million for CB2 and CB3); many series aren't so lucky, and see steep declines or fluctuations with each new episode, even when they're objectively better, and especially when they don't fundamentally change or expand the formula too much. See Donkey Kong Country or Zelda for instance.
- selling extremely well in Japan, something most Western games - let alone platformers - can only dream of achieving even today
It helps that the price is fair and the collection is, on the whole, extremely faithful to the original titles. Ubisoft Turtles in Time this ain't, no weird remake shenanigans here.