I grew up with the Sega Genesis, PS1 and then PS2. The PS1 side had games that were more lively, less lonely than SM64. Compare the game to something like even the first Spyro the Dragon, and SM64 immediately feels empty. Add to that the overtly creepy level Big Boo's Mansion, or the less creepy Hazy Maze Cave, or the surreal Wet Dry Town with the creepy cave music, the infinite stairs at the top of the castle, rooms that are huge but sport almost nothing except paintings, only a single big clock, a population of only one or two servants to the princess, levels like Lethal Lava Land which is just otherwise inhabitable platforms on top of a lava ocean - the game ends up feeling creepy whether the ~~programmers~~ lawyers at Ninten intended or not. How about the room with the Tiny Big Island paintings, one side is huge while the other side's wall is within arm's reach? Also Mario is always being recorded by the Lakitu cameraman, and you're watching him through that lens.

Besides, creepypastas were all the rage during the 2010s, and the 3D Mario had just enough ingredients to make them work - the ultimate culmination of all this being the B31133 romhack. (Correct me if I got the numbers wrong).