Garchomp is definitely more common and is generally the better pick. It has better Speed and Attack, better coverage options, and Dragon typing is generally better defensively. Resisting Fire and taking neutral damage from Water and Grass is worth the worse Ice weakness, and Krookodile's Dark typing doesn't do that much defensively since the main Psychic in the format has Fairy STAB too.
Krookodile is worse against Tapu Lele than Garchomp. Since Tapu Lele is part Fairy it only takes neutral damage from Crunch, and Krookodile doesn't have many good coverage options. Garchomp's Poison Jab does a good bit more to Tapu Lele than Krookodile's Crunch because it's super-effective and Garchomp has higher attack. Garchomp is also naturally faster than Tapu Lele, while Krookodile is naturally slower.
That logic doesn't quite hold up. Yes, people are more used to seeing Garchomp than Krookodile. But people still know what Krookodile does, and Garchomp has more viable move options which actually makes it less predictable.
Kinda irrelevant, Oranguru is not a major meta threat and Krookodile isn't a one-mon answer anyways (doesn't OHKO, hit hard by common partners)
If you're searching for reasons to justify using Krookodile, there's one big one: Role compression. If you want Intimidate, Arcanine is basically better than Krookodile. If you want a fast Ground-type, Garchomp is basically better than Krookodile. Those are the top two mons in the usage stats because those are valuable roles and most of the time they'll be the best picks for those roles. Krookodile sees use because even though its worse than Arcanine and Garchomp in those two roles, it combines them. If you build a team and you end up needing Intimidate and a fast Ground-type and you only have one free slot, Krookodile is your guy. It can also be the best choice for Intimidate if you want to use Marowak and Tapu Fini, for example. Arcanine and Gyarados would have overlapping types, Salamence would be weakened by your own Terrain, but Krookodile works fine with both of those.